organic chemistry · 2019-07-18 · the different types of organic compound, making them different...

NCEA | Walkthrough GuideLevel 2CHEMISTRY

11

Hydrogen

1.00794

H

321

Litium

6.941

Li

11281

Sodium

22.98976928

Na

192881

Potassium

39.0983

K

37281881

281882

28181881

2818321881

2818321882

28181882

Rubidium

85.4678

Rb

55

Caesium

132.9054519

Cs

87

Fransium

(223)

Fr

422

Beryllium

9.012182

Be

12282

Magnesium

24.3050

Mg

202882

Calsium

40.078

Ca

38

Strontium

87.62

Sr

56

Barium

137.327

Ba

88

Radium

(226)

Ra

212892

Scandium

44.955912

Sc

39281892

2818102

281832102

28183232102

2818122

281832112

28183232112

28181892

28181992

2818321892

Yttrium

88.90585

Y

2228102

Titanium

47.867

Ti

40

Zirconium

91.224

Zr

72

Hafnium

178.49

Hf

104

Rutherfordium

(261)

Rf

2328112

Vanadium

50.9415

V

41

Niobium

92.90638

Nb

73

Tantalum

180.94788

Ta

105

Dubnium

(262)

Db

57

Lantanum

138.90547

La

89

Actinium

(227)

Ac

58

Cerium

140.116

Ce

90

Thorium

232.03806

Th

CH

NN N

O Ph

ORGANIC CHEMISTRY

Introduction 3

Naming and Drawing Organic Compounds 4

The Main Carbon Chain 6Functional Groups 7Branch Chains 8Numbering Carbon Atoms 9Drawing Organic Molecules 10

Functional Groups 11

Organic Compounds with just Carbon and Hydrogen 12Organic Compounds with other Atoms Attached 15Acidic and Basic Organic Compounds 19Primary, Secondary and Tertiary Molecules 21

Isomers 23

Molecular Formulae 23Structural Formulae 24Structural/Constitutional Isomers 24Geometric Isomers 26

Organic Reactions 29

Addition Reactions 30Markovnikov’s Rule 33Elimination Reactions 34Reverse Markovnikov’s Rule 38Oxidation Reactions 39Substitution Reactions 41Neutralisation Reactions with Carboxylic Acids 43Acid-Base Reactions involving Amines 44

Polymers 46

Polymerisation Reaction 46

Properties of Organic Compounds 48

Introduction to Polarity 48Polarity of Organic Compounds 51Introduction to Melting/Boiling Point 53Melting/Boiling Point of Organic Compounds 54Introduction to Solubility 56

Level 2 Chemistry | Organic Chemistry

Level 2 Chemistry: Structure and BondingCram Guide

Solubility of Organic Compounds 56

Identification Tests 58

Red and Blue Litmus Paper 58Dichromate or Permanganate Solution 59Bromine Water 61

Key Terms 63

4 Level 2 Chemistry - Organic Chemistry | © Inspiration Education Limited 2017. All rights reserved.


This standard is all about carbon.

Well, the name of this standard is actually “organic chemistry”, but as you’ll see, that basically means we’re dealing with carbon atoms. These versatile atoms give us stuff like alcohol, vinegar, petrol, and all sorts of handy things.

“Organic” is a term that is thrown around a lot these days: organic farming, organic foods and so on - none of which have anything to do with the organic chemistry we’re about to get stuck into. So, what does it really mean? Organic chemistry is basically the study of hydrocarbons, the carbon and hydrogen molecules that are vital to life on Earth. The molecules that we are composed of and the molecules we rely on for food and our survival are mostly organic. In fact, the DNA that encodes all our genetic information is just one big, long organic molecule!

I guess you could say that if you understand organic chemistry, you understand life…

What will you learn in this walkthrough guide?

There’s a whopping 9 million different organic compounds, give or take a few, and you have to MEMORISE THEM ALL!

Just kidding! But we’ll begin the guide by looking at the conventions used to name all of these organic molecules, looking at things like the number of carbons they have and what other kinds of atoms they have hiding away.

From there, we will look at some of the basic functional groups, how to name each one, how different functional groups are different from one another, and what kind of properties they all have.

After this we’ll go off and talk about these things called isomers and how we can identify whether two molecules are isomers.

The next section is the core of organic chemistry: the organic reactions. Often dreaded by most chemistry students, we can classify each reaction into addition, elimination, substitution and oxidation reactions, and then look at the different types of reactions each functional group is involved in. By the end of it you will be able to draw up a nice flow chart showing how to use organic reactions to get from one functional group to another.

We’ll also spin a few yarns about these things called polymers and end with identification tests which are ways to identify what kind of organic molecule you have in your beaker.

INTRODUCTION

Level 2 Chemistry - Organic Chemistry | © Inspiration Education Limited 2017. All rights reserved.5


A word on exam strategy.

Organic Chemistry is a MASSIVE external topic and so there is a lot to take in. But the idea is that you should be able to make links between each concept or idea, rather than thinking about everything as separate, individual topics.

Here at StudyTime, we’re pretty much GCs (good citizens), so to help you out, we’ve made this guide in plain English as much as we can. We’ve also included a glossary for some of the key terms that you’ll need to master for your exam.

However, the language we use isn’t always something you can directly write in yourexam. When this is the case, we offer a more scientific definition or explanation (in ahandy blue box) underneath. These boxes are trickier to understand on your first readthrough, but contain language you are allowed to write in your exam. Look out forthem to make sure you stay on target!

NAMING AND DRAWING ORGANIC COMPOUNDSI have a name; my dog has a name and hopefully you have a name too. It’s nice having a name. It’s a lot better than being referred to as “it” or being rudely pointed at. It’s only fair that organic compounds have names as well.

Naming and drawing organic compounds is a super duper important aspect of this external. 10/10 would recommend making sure you ace this section before moving on.

There are two main parts to any organic molecule name:

1. The part that tells us how many carbon atoms there are in the main carbon chain (we’ll look at this in the next section)

2. The part that tells us what kind of organic compound it is.

To make sure you actually learnt a thing or two, after reading this section make sure you understand:

How to determine the length of the main carbon chain and use this to get the right prefix. What functional groups are.



What branched groups are, and how they are included in the name of an organic compound.How to choose the right end of the molecule to start numbering the carbon atoms from. How to go about drawing one of these organic molecules.

The Main Carbon Chain

Organic compounds are no cowards, they’ve all got a spine – a spine of carbon atoms, that is. The main carbon chain (sometimes called the “backbone”) is the most important part of the molecule as all the other atoms that make the molecule special and unique attach to these carbon atoms.

To name an organic compound the first thing to do is the identify the longest, continuous chain of carbon atoms

This seems a bit pedantic but it’s for good reason. Sometimes there can be smaller carbon chains that branch off from the main chain – so only count the largest chain.

Other times the carbon chain gets so huuuge that it starts to bend and make corners – in this case the chain is still continuous.

longest carbonchain

longestcarbonchain

longest carbon chain

H

C

H

H

C

H

HH H

C

H

C

C

H

H

H

C

H

H

C

H

H H

H H

H

C

H

H

C

H

H

C

H

H

C

C

H HC

H

H

C

H

HH

H

C

H

H

C

C

H

C

H

H

H H

C

H

H H

H

Since carbon has 4 valence electrons it will form 4 covalent bonds. This means that you should always have 4 atoms around it. First connect all the carbon atoms together, and any remaining bonds are filled by bonding to hydrogen atoms.

To get the first part of the name just count the number of atoms and find the corresponding prefix. (The prefix is just a fragment of a name that goes at the beginning). Have a peek at the table below to help you:



Number of Carbon Atoms

Prefix Alkane Example Side Group

1 Meth- Methane Methyl2 Eth- Ethane Ethyl3 Prop- Propane Propyl4 But- Butane Butyl5 Pent- Pentane Pentyl6 Hex- Hexane Hexyl7 Hept- Heptane Heptyl8 Oct- Octane Octyl9 Non- Nonane Nonyl10 Dec- Decane Decyl

Unfortunately learning some of the prefixes on this table is a matter of memorisation. We will, however, give you one hint: After the first 4, the rest of prefixes correspond to the shapes with the same number of sides.

For example, a pentagon has 5 sides and a pentane molecule has 5 carbons.

STOP AND CHECK:

Turn your book over and see if you can remember:

How to identify the main carbon chain of an organic molecule. Which prefix to use based on the number of carbon atoms there are in the

main carbon chain – aim to recreate the table we used.

Try to explain it in your own words.

Functional Groups

So, we’ve looked at the carbon chain - the most important part of the molecule. Now that we’ve got this sorted, let’s look at the other component of an organic molecule: the functional group.

The simplest organic molecules are called the alkanes

Alkanes are composed entirely of carbon and hydrogen atoms, all connected using just single covalent bonds.

Other organic compounds are more complicated, and have different functional groups.



These functional groups, like double bonds, hydroxyl (-OH) or halogen atoms, represent the different types of organic compound, making them different from the rest.

They affect the chemical and physical properties of the compound.

Since they’re pretty important they have a shout-out in the molecule name. Give it a few pages and we’ll touch upon the corresponding prefixes and suffixes (fragments of the name that go right at the end) for each functional group.

Functional groupH

C

H

OH

C

H

H

C

H

H

C

H

HH H

C

H

H

C C

H

H

C

H

HH

Cl

C

H

H

C

H

H

C

H

H

C

H

HH

STOP AND CHECK:


What functional groups are, including a few examples.


Branch ChainsAlthough we said that molecule names have two parts to them, sometimes there’s an additional part. Remember how we said that some organic molecules have smaller carbon chains that branch off from the main one? It’s not fair to ignore them, so we give them a consolation prize for trying. These are known as side groups.

The main side groups you will be dealing with are the methyl side groups (with one branched carbon) and the ethyl side groups (with two branched carbons). Sense a bit of a pattern? The groups are named using the same prefixes that we use to name our carbon chains - and can be checked out in the same table as before!

branched groupmethylgroup

ethylgroup

H

C

H

H

C

H

H

C

CH3

H

C

H

H

H

CH H

longest chain

H

C

H

H

C

H

H

C

HH H

H

H

C

C

H HC

H

H

CH C

H

C

H

H

H

H

longest chain



STOP AND CHECK:


What branched chains or side groups are. How to name branched chains or side groups, using the table from the “Main

Carbon Chain” section.


Numbering Carbon Atoms

When it comes to a molecule, it’s important that you know where everything is.

To help us find functional groups or side chains, we number the carbon atoms in the main chain

Whatever carbon number they’re attached to will be included in the name.

Although it’s tempting just to number the carbon atoms from left to right, this won’t always get you the correct answer. Instead, you need to number from both ends and use the one that makes the functional groups or side chains end up on the lowest numbered carbon atoms, rather than the biggest.

Cl on Carbon 4

wrong numbering

CH3 CH2 CH2 CH

Cl

CH3

1 2 3 4 5

Cl on Carbon 2

CH3 CH2 CH2 CH

Cl

CH3

5 4 3 2 1

correct numbering

STOP AND CHECK:


How to determine the correct end of the molecule to start numbering carbon atoms from.




Drawing Organic Molecules

As well as naming organic molecules, it is equally important for this standard that you know how to draw them.

The first step in drawing organic molecules is to draw the main carbon chain

The number of carbon atoms in the molecule is indicated by the prefix in the name.

prop ane

3 carbons

prefix

hex anol

6 carbons

prefix

but anoic acid

4 carbons

prefix

The next thing to draw is any functional groups or side groups on the organic compound

The appropriate prefix or suffix are used depending on the functional group as well a number indicating their position on the chain.

prop� an–2– ol

prefix = no. of cabons

suffix = functional group

3– chloro pent ane

1st prefix = functional group

2nd prefix = no. of carbon atoms

position of functional group

position of functional group

suffix = functional group

STOP AND CHECK:

Have a go at drawing the following organic molecules:

Pentane Methane A pentane molecule with a methyl group on the 2nd carbon atom. A pentane molecule with an ethyl group on the 3rd carbon atom.

Quick QuestionsConsider the following organic compound:

H

C

H

H

C

H

H

C

H

HH



What is the prefix used for this molecule based on the number of carbon atoms in the main carbon chain?

Consider the following organic compound:

CH3

CH CH2CH3 CH3

How many carbon atoms are in the main carbon chain? What is the prefix used for this molecule based on the number of carbon atoms in the main carbon chain?

How many branched chains, or side groups, are there? Which carbon atoms are they on?

What is the name given to each of the side groups based on the number of carbon atoms there are?

FUNCTIONAL GROUPSThe idea of functional groups was introduced right at the start. These are the important bits of each organic molecule, and may include double or triple bonds, single atoms like halogens, or small groups of atoms like hydroxyl, carboxyl and amine groups. Sound like a bit of a heavy list?

Don’t worry! In this section we’ll run through each functional group in more detail as well as how to name them.

So, by the end of this section you should be familiar with:

The ‘basic’ organic compounds - those with just carbon and hydrogen - and how to name them. The organic compounds with a few exciting atoms attached - haloalkanes and alcohols - and how to go about naming them. `The acidic and basic organic compounds - carboxylic acids and amines - what makes them acidic/basic and what to call them. We’ll finish things off by looking at a way of classifying haloalkanes and alcohols.

Organic Compounds with just Carbon and Hydrogen

Take some Carbon and Hydrogen atoms, mix them together, and you get yourself an alkane.



With just two types of atoms, and only single covalent bonds throughout the molecule, alkanes are the simplest, and therefore the most boring, organic compounds.

However, throwing together some carbon and hydrogen atoms might not always get you an alkane.

That’s because alkenes and alkynes are also made up of just carbon and hydrogen atoms

There’s just one small thing that makes alkenes and alkynes different from alkanes. Imagine the carbon atoms in the carbon chain of alkanes as colleagues, and nothing more. They’re happy with forming a covalent bond with one another, but only because they want to get the job done.

In alkenes, two of the carbon atoms are more than just colleagues, they become friends. Rather than just having a single covalent bond between them, they have 2, which is referred to as a double bond. It’s their way of getting closer to one another.

H

H

C CH

Hdouble bond

If all the carbon atoms in alkanes are just colleagues, and two carbon atoms in alkenes are friends, in alkynes two of the carbon atoms are best friends! That’s because things get a lot more close and personal with the presence of at least 1 triple carbon-carbon covalent bond.

CH HC

triple bond

Alkenes have at least one double bond, while alkynes have at least one triple bond.

Naming Alkanes:

It would be rude to just point, and it would be even more rude to refer to all organic compounds as “it”, so we better learn their names. When it comes to naming alkanes, there are two parts to their name:



1. The number of carbon atoms in the backbone determines the ‘prefix’ of the alkane name. So, if you chuck on 3 carbons atoms it would have the prefix, “prop-“.

2. All alkanes end with the suffix, “-ane”. Using the same example as above, an alkane with 3 carbons would be called “propane”.

H

C

H

H

C

H

H

C

H

HH

propane

Naming Alkenes:

Naming alkenes is pretty standard. The thing that unites all alkenes is the suffix, “-ene”, which gets thrown on at the end of the molecule’s name.

The start of the name comes down to the number of carbon atoms in the main carbon chain, where one carbon is “meth-“, two carbon atoms is “eth-“, and so on.

In alkenes, any two of the carbon atoms can form a double covalent bond and become friends, so it’s important to say who’s getting friendly with who in the molecule name. To indicate the position of the carbon-carbon double bond, take the lowest numbered carbon of the two carbon atoms involved, and slot the number between the prefix and “-ene”.

So, if there’s a double bond between the 1st and 2nd carbon atoms in an alkene with 5 carbons, its name will be “pent-1-ene” (not pent-2-ene).

HH

C

HH

H

C

H

H

C

H

H

H

C HC

pent-1-ene

So, if there’s a double bond between the 2nd and 3rd carbon atoms in an alkene with 4 carbons, its name will be “but-2-ene” (not but-3-ene).

H

C

H

H

C C

H

H

H

C HH

but-2-ene



Naming Alkynes:

By now you’ll hopefully be getting used to naming organic compounds. Figuring out the prefix based on the number of carbon atoms in the main chain should be no problem.

When it comes to naming alkyne molecules, the suffix is “-yne”.

Just like with the double bond in alkenes, you must include the position of the triple bond, and put the number position between the prefix and “-yne”.

H C C

H

H

C H

propyne

Saturated and Unsaturated Haloalkanes

If you’ve ever had the misfortune to be lectured about your health and wellbeing, you may have heard the terms, “saturated” and “unsaturated”, being thrown around, especially when talking about fats. Well, these terms can be used to classify many organic compounds.

In fact, all alkanes are said to be saturated

It’s not because they’re soaking wet, it’s because all carbon-carbon bonds are single bonds, and there are no carbon-carbon double or triple bonds at all.

CH

H

H

H

H

C H

ethaneCC

H

H

H

H

H

H

C HH

propane

CC

H

H

H

H

H

H

C C

H

H

HH

butaneCC

H

H

H

H

H

H

C C

H

H

C

H

H

HH

pentane

All these alkanes above have single bonds - no double or triple bonds present.



Remember, carbon atoms have 4 valence electrons so must form 4 and only 4 covalent bonds.

When two carbon atoms form a double bond in alkenes they must each ditch 1 hydrogen atom to make some room. Because two hydrogen atoms were removed to make way for the friendship-forming double covalent bond, alkenes do not have only single carbon-carbon bonds, and are therefore unsaturated.

C

H

H

H

H

C

ethene

CC

H

H

HH

H

C H

propene

CC

HHH

H

C C

H

H

HH

but-2-ene

The alkenes above have at least one double bond - not all of their covalent bonds are single ones.

This is the same for alkynes as they have at least one triple carbon-carbon bond - they are also unsaturated.

Unsaturated molecules have at least one double or triple bond.

Friendships may not last forever, and it turns out the second carbon-carbon bond in the double bond of alkanes, or the second and third carbon-carbon bond in alkynes, is easier to break than a standard single carbon-carbon covalent bond.

This makes alkynes and alkenes more reactive than alkanes.

STOP AND CHECK:


How to name alkane molecules. What is meant by the terms, “saturated” and “unsaturated”. Are alkanes

saturated or unsaturated? The functional group present in alkenes. How to name alkene molecules. The functional group present in alkynes. How to name alkyne molecules.




Organic Compounds with other Atoms Attached

Some say that simplicity is the ultimate form of sophistication. That may be true, but when it comes to organic compounds, there needs to be more excitement than just carbon and hydrogen atoms. So, it’s time to mix things up!

Haloalkanes look an awful lot like alkanes, except for one little key difference: an intruder lurks within the main carbon chain. This intruder is a halogen atom.

Halogens are a special group of elements found way down in Group 17 of the Periodic Table of Elements...

...starring fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). Just having this one halogen atom attached to one of the carbon atoms is a complete game changer, altering the physical and chemical properties.

possible halogen atomsto make a haloalkaneCC

HH

H

C

H F

I

ClBr

HH

H

Haloalkanes are alkanes which are bonded to at least one halogen atom.

Naming haloalkanes is a little trickier than with other organic compounds. Unlike with alkanes, alkenes and alkynes, the unique part of a haloalkane’s name is a prefix rather than a suffix.

Secondly, the prefix used actually depends on what halogen atom is attached

So, if it’s fluorine it would be “fluoro-“, if it was chlorine you’d use “chloro-“, for bromine “bromo-“, and in the unlikely event that iodine is present, you’d need to use “iodo-“. This goes at the start of the name.

Next comes the part of the name which tells us how many carbon atoms are in the main chain, and it ends with “-ane”.

Because the halogen atom can go on any of the carbon atoms it’s important to also say where it is on the molecule. For example, a haloalkane with a chlorine atom attached to the 2nd carbon in a 5-carbon chain would be called “2-chloropentane”.



2 - chloropentane

e.g. CH3 CH

Cl

CH2 CH2 CH3

Sometimes we may get two halogens - either two of the same halogen atom or two different ones.

When you have two different halogen atoms you simply pile up the prefixes on top of each other, and put them in alphabetical order. For example, if there is a butane with a bromine on carbon 1 and a chlorine on carbon 2, you will have 1-bromo-2-chlorobutane (not 2-chloro-1-bromobutane).

When you have two of the same halogen atoms you first list all the carbon numbers involved with bonding to these atoms, and then you use di- when there are two of the same halogen or tri- when there are three. For example, a propane chain with two chlorine atoms, both on carbon 1, would be called 1,1-dichloropropane.

1 - bromo, 1 - chlorobutane

1, 1 - dichloropropane

e.g.

e.g.

Br CH2

Cl

CH CH2 CH3

Cl

ClCH CH2 CH3

Alcohol molecules contain the hydroxyl functional group

This hydroxyl group is composed of an oxygen covalently bonded to a hydrogen atom (-OH). This -OH group can be bonded to any one of the carbon atoms in the main chain.

This little hydroxyl group does wonders, drastically changing the properties of alcohol molecules compared to other functional groups. That’s because the -OH is highly electronegative and makes small alcohol molecules polar. Don’t worry if those concepts sound a little scary right now - we’ll look into them in depth later on!

Naming Alcohol Molecules:

To name alcohol molecules we use the suffix, “-anol”, which goes at the end of the molecule’s name.

The position of the hydroxyl group must also be shown in the name, which is represented



by a number. This number goes in between the “an” and the “ol” of “-anol”.

For example, an alcohol with the -OH group attached to the 2nd carbon of a 3-carbon chain is called “propan-2-ol”.

propan - 2 - ol

hydroxyl (-OH) groupCH3

OH

CH CH3

Why stop at just 1 hydroxyl group, why not add another one for the yarns?

Alcohol molecules with 2 hydroxyl (-OH) groups attached to the main chain are called diols

Not a whole lot changes and they still act the same as normal alcohol molecules. The only difference is that they are slightly more polar, giving them a higher melting/boiling point and greater solubility in water.

The real fun comes in their naming

The first part of the name is the name of the alkane which would form from the diol’s main carbon chain.

The second part of the name is the suffix, “-diol”. A diol with an -OH group on the 1st and 2nd carbon of a 3-carbon chain would be called, “propan-1,2-diol”.

propan - 1, 2 - diolCH3

OH OH

CH CH2

STOP AND CHECK:


Where the halogen atoms are found on the Periodic Table. The common halogen atoms. The prefixes used for haloalkanes containing:

• Fluorine• Chlorine• Bromine• Iodine



The name of the functional group in alcohols. The atoms that make up the functional group of alcohols. How to name alcohol molecules. The structure of a diol – what’s the difference between an alcohol and a diol. How to name diol molecules.


Acidic and Basic Organic Compounds

So far all our organic compounds have been pretty boring considering they are all neutral in solution. Carboxylic acids change this!

Carboxylic acids are acidic

These organic compounds contain an acidic functional group, the carboxyl (-COOH) group, making them acidic. In a carboxylic acid, the end carbon in the main chain is covalently bonded to two oxygen atoms, one with a double bond and one to an OH group - this represents the carboxyl group.

H

H

H

C

H

H

C

H

H

CO H

OC

carboxyl group

To make sure we’re all on the same page:

Acids are defined as proton donors

This means that the acid releases a hydrogen ion (H+), equivalent to a proton.

In carboxylic acids, the hydrogen ion comes off from the carboxyl group - the hydrogen atom that’s on the hydroxyl (-OH) group. When the hydrogen is removed from the carboxyl group it leaves behind the carboxylate group: COO-.

CH3 + H

++

HCH2 O

O

O H

OC

CH3 CH2O- H

O H HC

(H2O / water)

(H3O+ / hydronium ion)

proton (H+) is donated



With carboxylic acids being the only acidic organic compound in Level 2 Chemistry, it is only fair to have a basic one as well.

Amines contain an -NH2 group attached to one of the carbon atoms in the main carbon chain

The main property of amines is that they are basic

To make sure we’re all on the same page, bases are defined as proton acceptors, where the base receives a hydrogen ion (H+), or proton, from an acid. If you need a bit of revision, head over to the Level 2 Chemical Reactivity guide.

In amines, the hydrogen ion attaches to the nitrogen forming NH3+ which is attached

to one of the carbon atoms.

CH2 + H

++ -

HCH3 CH2 O

HO

H

HN

CH2CH3 HCH2

H

HN

(H2O / water)

(OH- / hydroxide ion)

proton (H+) is accepted

Naming Carboxylic Acids and Amines:

To name a carboxylic acid you must count the number of carbon atoms in the main chain, just like you have been. This gives the prefix of the molecule’s name.

Carboxylic acids end with “-anoic acid”

However, unlike other functional groups, the carboxyl group can only be attached to the 1st carbon atom in the main chain. Therefore, we don’t need to indicate its position.

For example, a carboxylic acid with a 4-carbon chain would be called “butanoic acid”.

butanoic acidCH3 CH2 OH

OCH2 C

4 3 2 1

This position of the carboxyl group is important. Even when other functional groups are present, the carboxyl group is ALWAYS on the first carbon, and it trumps all other functional groups. So start numbering the carbon atoms in the chain from here.



For example, if there is a 3-carbon chain with a bromine on one end and a carboxyl group on the other, the molecule will be called 3-bromopropanoic acid. You must always start numbering from the carboxyl group.

3 - bromopropanoic acidBr CH2 OH

OCH2 C

3 2 1

When it comes to naming amines you can either use the prefix, “amino-“, or the suffix, “-amine”

By now you should know that you must indicate which number carbon atom the amine group is attached to.

For example, an amine with the -NH2 attached to the 1st carbon of a 3-carbon chain may be named “propan-1-amine” or as “1-aminopropane”.

Either is acceptable, although sometimes you may be forced to use one or the other depending on other functional groups present. However, using it in the beginning is always fine, so if in doubt just use that one. And, if they give you an example of an amine in the exam it will be written both ways so you shouldn’t get confused!

propan-1-amine” or “1-aminopropaneCH3 CH2 CH2 NH2

3 2 1

STOP AND CHECK:


The atoms which make the carboxyl group. How to name carboxylic acid molecules. Why it is not necessary to indicate the position of the carboxyl group

in carboxylic acid molecules. Why the carboxyl (-COOH) functional group is said to have acidic properties. What atoms make up the amine group. The prefix and suffix that can be used to name amines. Why the amine (-NH2) group has basic properties.




Primary, Secondary and Tertiary MoleculesNow that we’ve met each of the different functional groups associated with organic molecules, let’s go one classification further - and look at how haloalkanes and alcohols can be classified into ‘Primary’, ‘Secondary’ and ‘Tertiary’ molecules.

These words are just a fancy way of saying “1, 2, 3”

Starting with haloalkanes, primary haloalkanes are molecules where the halogen atom is bonded to a carbon atom which is then bonded to just 1 other carbon atom. With secondary haloalkanes this carbon atom is bonded to 2 other carbon atoms, and with tertiary haloalkanes this carbon atom is bonded to 3 other carbon atoms.

The classification is important because it changes the properties of the molecule slightly.

primary haloalkane

CH3 CH2 CH2 Cl1

secondary haloalkane

CH3 CH CH3

Cl1 2

tertiary haloalkane

CH3

CH3

C CH3

Cl1 2

3

Just like haloalkanes, alcohols can be classified as primary, secondary and tertiary alcohols, depending on how many carbon atoms the carbon attached to the -OH group is bonded to.

primary alcohol

CH3 CH2 CH2 OH1

secondary alcohol

CH3 CH CH3

OH1 2

tertiary alcohol

CH3

CH3

C CH3

OH1 2

3

When it comes to primary, secondary and tertiary alcohols, there are some very important differences in properties that you need to be aware of. For now, be familiar with the classification - and we’ll introduce some important properties of them when we get into reactions later on!



STOP AND CHECK:


Which types of alcohol molecules can be oxidised and which ones cannot. What are primary, secondary and tertiary haloalkanes? What is the difference

between them?


ISOMERSOrganic molecules are formed when different atoms come together and form covalent bonds. Sometimes, we can end up with some very similar looking molecules that aren’t quite identical. This happens when the same number and type of atoms come together to form a different molecule by changing up the way they bond to one another.

Basically, you start off with the same ingredients - but can get a range of different outcomes.

These different outcomes are known as isomers

It’s best to define isomers as, “organic molecules with the same molecular formula (same number and type of atoms) but a different structural formula”.

There are two main classes of isomers:

1. Structural (Constitutional) Isomers2. Geometric Isomers

Now that we established what isomers are, what do you need to know about them:

Before jumping into the deep end, take a moment to understand the structural and molecular formulae, and what they tell us. What are structural isomers? What kinds of structural isomers are there? What are geometric isomers, and how do they differ from structural isomers?



Molecular Formulae

The molecular formula of an organic compound tells us the exact number and type of atoms present

This is done by using the symbol for each atom followed by a subscript (a small number) which indicates how many of each particular atom there is. So, the molecular formula for propane is: C3H8.

Using molecular formulae has its downsides because it doesn’t tell us how these atoms bond to one another. That’s why we can end up with heaps of different organic molecules with the same molecular formula (isomers).

STOP AND CHECK:


What the molecular formula of a molecule tells you. Why different molecules can have the same molecular formula.


Structural FormulaeJust like with molecular formulae, you are probably already familiar with structural formulae as well. They are what we’ve been using to draw our organic compounds.

A structural formula shows the actual number and type of atoms, and shows how they are all bonded together to form a compound. For propane you’d give it the structural formula: CH3-CH2-CH3.

STOP AND CHECK:


What the structural formula of a molecule tells you. The difference between the structural and molecular formulae.


Structural/Constitutional Isomers

Structural isomers (also commonly known as constitutional isomers) are isomers which have the same molecular formula but a different structural formula.



So, the same number and type of atoms as one another, but these atoms are bonded differently. Structural isomers can be grouped into 3 different types:

1. Positional Isomers

These are structural isomers where the position of a functional group or a side chain is different. When functional groups or side chains are moved, and placed on a different carbon atom in the main chain, the structural formula becomes different.

For example, propan-1-ol and propan-2-ol are positional isomers as the hydroxyl (-OH) group is on the 1st carbon atom in t but on the 2nd carbon atom in propan-2-ol.

propan-1-ol propan-2-ol

CH3 CH CH3

OH

CH2 CH3 CH3

OH

1 2 3 1 2 3

2. Branched Chain Isomers

These are structural isomers where the main carbon chain is of a different length due to the formation of side chains, such as methyl or ethyl groups. As side chains are added, or as side chain lengths are increased, the length of the main chain decreases to keep the number and type of atoms the same in all isomers.

For example, butane and methylpropane are chain isomers. Butane has 4 carbons in its main chain, while methylpropane has 3 carbons in its main chain. However, methylpropane has a methyl group on the 2nd carbon, giving it 4 carbons (and 10 hydrogens) in total – the same as butane.

4 carbons, 10 hydrogens

butane 2,methyl-propane

methyl group


CH3 CH CH3

CH3

CH3 CH2 CH2

1

CH3

42 3 1 2 3

3. Functional Group Isomers

Functional group isomers are an interesting type of structural isomer that do not occur that often in Level 2 Chemistry. These are structural isomers where the same number and type of atoms have been arranged in such a way that different functional groups have been formed.



For example, butene and cyclobutane are functional group isomers.

• Butene is an alkene with 4 carbon atoms in its main chain, with a double bond occurring between two of the carbon atoms. This leaves 8 hydrogen atoms attached.

• In cyclobutane, the 4 carbon atoms form a ring structure where the first and last carbon atoms are bonded to one another. With every carbon bonded to two carbon atoms, there are two bonds available for hydrogen atoms, giving cyclobutane 8 hydrogen atoms in total.

• Both butene and cyclobutane have the same molecular formula (C4H8) but each has a different functional group (butene is an alkene, while cyclobutane is a cycloalkane).


but - 2 - ene cyclobutanedouble bond


H HH

HHH

H

HCH3 CH

C

CCC

CH1 3

4

2

CH3

42 3

STOP AND CHECK:


What structural isomers are. The differences and similarities between positional isomers, branched chain isomers

and functional group isomers.


Geometric Isomers

Sometimes the bane of a chemistry student’s existence, geometric isomers are tricky at first to get your head around. So, pay close attention to this next section!

Let’s begin by defining them:

Geometric isomers are molecules with the same molecular formula and the same structural formula.

Uh oh! At first, this seems a bit strange because if they have the same structural formula and their atoms are bonded in the exact same way, they must be the same molecule. However, geometric isomers differ in how the atoms, functional groups and/or side



chains are positioned around a carbon-carbon double bond. This is because:

Single covalent bonds allow free rotation of the atoms involved

However, when it comes to double bonds, this rotation is prevented.

In alkanes, where there are only single carbon-carbon bonds, the atoms do not have a fixed position and everything is free to spin around as it pleases. This means that, even though molecules may look different, they can easily twist in space to look the same as each other again.

But when a double bond is added, particular positions of atoms are fixed, making it possible to have molecules with different geometric arrangements; an example of isomerism!

rotation

OR

H3CH Cl

HH

HOC

H

CH3

CH3

HC C

C

single bond(can be freely rotated)

double bond(prevent free rotation)

H3CH H

ClH

HOC C

rotation

H3CHO H

ClH

HC C

CH3

H

H

CH3

C C

There are 3 requirements that a molecule must meet before it can exist as a geometric isomer:

1. There must be a carbon-carbon double bond present to prevent free rotation in space. In Level 2 Chemistry this basically means geometric isomerism only occurs with alkenes.

2. Each carbon attached to the double bond must have two different groups bonded to it.

3. There must be a common group on each side of the double bond.

CH3

H

CH3

ClC C

1. carbon-carbondouble bond

3. a common group

2. each carbon is attached to 2 different groups

This molecule canexist as a geometric isomer



With geometric isomerism, the atoms or groups of atoms around a double bond can either be fixed in the ‘up position’ or the ‘down position’.

When two identical groups are on the same side around the double bond (i.e. both in the ‘up’ position or both in the ‘down’ position) we get a cis-isomer. To name a cis-isomer simply add the “cis-“ prefix in front of the molecule’s name.

common groups on the same side

cis - isomer — cis - 1,2 - dichloroethene

H

Cl

H

ClC C

When two identical groups are on opposite sides around the double bond (i.e. one in the ‘up’ position and one in the ‘down’ position) we get a trans-isomer. To name a trans-isomer simply add the “trans-“ prefix in front of the molecule’s name.

hydrogens on opposite sides AND

trans - isomer — trans - 1,2 - dichloroethene

H

Cl

Cl

HC C

chlorines on opposite sides

H

Cl

Cl

HC C

A nice way to remember how to get the right prefix for the two geometric isomers, remember “cis” for “cisters” and “sisters stick together”, so the same atoms/groups will be on the same side. Then, the alternative with the same atoms/groups on opposite sides must then be the trans-isomer.

STOP AND CHECK:


What geometric isomers are and how they differ from structural isomers. The 3 requirements for geometric isomerism to occur. How to name geometric isomers.




Quick QuestionsConsider the following molecule: pentane

What is its structural formula? What is its molecular formula? What do the structural and molecular formulae tell you about the molecule?

Consider the molecular formula: C4H9Cl

Draw the organic molecule containing 4 carbons in the main carbon chain. Draw as many branched-chain isomers as you can with the same molecular formula. From the branched-chain isomers you drew, are any of these positional isomers? Why, or why not?

Draw the functional group isomer with the same molecular formula.

Consider the following two molecules:

and

CH3

CH CH3

CH3

CH3CHCH CH3CH3

CCl

Which molecule above can form geometric isomers, and which one cannot, giving reasons for your answer.

ORGANIC REACTIONSOrganic chemistry loves to classify stuff, and when it comes to organic reactions this is no exception. If you didn’t have enough to learn, these reaction types are important because you might be required to state what kind of reaction has taken place, or simply define each type and compare between them.

There are 5 main types of organic reactions:

1. Addition reactions2. Elimination reactions3. Oxidation reactions4. Substitution reactions5. Acid-Base reactions

a. Neutralisation of carboxylic acidsb. Acid-base reactions of amines

For addition and elimination reactions there are sometimes two possible products, and

?



for these it’s important to take into account Markovnikov’s Rule, which we will cover in due time, don’t worry!

But, the most important part of this section (and ultimately the most important part of this external standard) are all the specific organic reactions involving the functional groups we have covered! For each of the 5 main types of organic reactions we will cover the reactions that you will need to know, including any reagents and reaction conditions required.

Addition Reactions

Okay, these reaction types are as straightforward as they sound – trust me, there’s no hidden complexities hiding beneath the surface.

Addition reactions just involve adding on new atoms to the original molecule

So, it’s easy to identify if an addition reaction has occurred because you’ll end up with more atoms.

The only way carbon atoms can get more atoms attached to them is if they break some of their current bonds.

In addition reactions the double or triple carbon-carbon bonds are first broken to make some room

In NCEA we really only deal with addition to double bonds because addition to triple bonds (in alkynes) can get messy pretty quickly. But just know all the same rules apply if you were to do this with alkynes.

chloroethane

e.g. CH2 = CH2 + HCl

Cl - CH2 - CH3

Cl - CH2 - CH3

CH2 CH2 CH2 H Cl+CH2 CH2 CH2double bound

breaksH and Cl atoms

are added

Although addition reactions only involve alkenes, there are 5 addition reactions you need to be aware of

The difference between them is the reagent that is added and the type of organic molecule produced as the product.

A reagent is a substance or compound which is added to a reaction in order to make it happen.



Reaction 1: Alkene to Alkane

The first addition reaction involves converting an alkene to an alkane. The difference between alkenes and alkanes is the presence of a double bond in the alkene. In order for a double bond to be formed between two carbon atoms, alkenes must have 2 less hydrogen atoms than alkanes of the same chain length.

4 carbons,10 hydrogens

4 carbons,8 hydrogens

CHH

HCH

HCH

HCH

HH

CHH

HCH

CH

CH

H

+H2

HCHH

HCH

CH

CH

HH

This means that if we want to convert an alkene to an alkane we need to add two hydrogen atoms. So, the reagent we’ll use is H2, which is how hydrogen gas exists normally. After breaking the double bond, one hydrogen bonds to each of the carbon atoms previously involved in the double bond.

But, this reaction isn’t that willing to go ahead. We need to give it a bit of a push in the right direction with a catalyst. Remember, catalysts are those things that speed up reactions by lowering the activation energy. For the addition of H2 to alkenes either a platinum (Pt) or nickel (Ni) catalyst can be used. Since they are catalysts they won’t be used up in the reaction.

Using ethene as an example, the overall reaction looks like: Pt/Ni catalyst

CH2 = CH2 + H2 → CH3-CH3

Reaction 2: Alkene to Haloalkane

The difference between alkenes and haloalkanes is that alkenes are unsaturated with a double bond, while haloalkanes are saturated and contain a halogen atom attached somewhere on the main carbon chain. When the double bond breaks between two carbon atoms in an alkene, both carbon atoms need to bond to one more atom to give them a full valence shell. To make a haloalkane, one carbon will be given a halogen atom (such as chlorine or bromine), while the other is given a hydrogen atom.

The two possible reagents that can be used in this equation are HCl or HBr. These molecules split into the hydrogen atom and the halogen atom (chlorine or bromine), and both are added to the carbon chain.



Using ethene as an example, the overall reaction looks like either:

CH2 = CH2 + HCl → CH3 - CH2 - ClCH2 = CH2 + HBr → CH3 - CH2 - Br

There are two carbon atoms in this reaction that need additional atoms added to them after the double bond breaks. How do you choose which one gets the halogen atom and which one gets the hydrogen? For this we will need to use Markovnikov’s Rule, covered after “Addition Reactions”.

Reaction 3: Alkene to Di-Haloalkane

This reaction is very similar to the last one we encountered. Rather than making a haloalkane with just one halogen atom attached, it is possible to make a haloalkane with two halogens. This means that, rather than using a hydrogen halide as a reagent (HCl or HBr), we use two halogen atoms.

Chlorine and bromine both exist as molecules: Cl2 and Br2. Cl2 splits into two chlorine atoms, or Br2 splits into two bromine atoms, and each one attaches to either of the carbon atoms previously involved in the double bond in the alkene.

Using ethene as an example, the overall reaction looks like either:

CH2 = CH2 + Cl2 → Cl - CH2 - CH2 - ClCH2 = CH2 + Br2 → Br - CH2 - CH2 - Br

Reaction 4: Alkene to Alcohol

Another addition reaction is the conversion of an alkene to an alcohol. Like all the reactions before now, it’s important to think how these functional groups are different: an alkene is composed of carbon and hydrogen atoms with a double bond between two of the carbon atoms; an alcohol is composed of a chain of carbon and hydrogen atoms, with a hydroxyl (-OH) group attached to one of the carbon atoms in the main chain.

Immediately, we know that somehow we need to get an -OH involved. When the double bond breaks between the two neighbouring carbon atoms, one of the carbons will get the hydroxyl group, while the other can get a stock standard hydrogen atom. Therefore, the reagent to use in this addition reaction is water (H2O)!

However, normal water won’t cut it

Instead, acidified water (H2O/H+) is added to the alkene.



Using ethene as an example, the overall reaction is: CH2=CH2 + H2O/H+ → CH3-CH2-OH

Just like with the alkene → haloalkane reactions, we run into the issue of deciding which carbon to give the hydroxyl group and which one to give the hydrogen atom. Again, we will need to use Markovnikov’s Rule, covered after “Addition Reactions”.

Summary

All addition reactions involve alkene molecules. They are addition reactions because the double bond is removed and new atoms or functional groups are bonded to the carbon atoms to fill their valence shell. These “new” atoms or functional groups come from the particular reagent added.

The following reagents can be used with alkenes:

1. Hydrogen gas (H2) with Pt or Ni catalyst to produce an alkane.2. HCl or HBr to produce a haloalkane (a chloroalkane or a bromoalkane). 3. Chlorine (Cl2) or bromine (Br2) to produce a di-haloalkane. 4. Acidified water (H+/H2O) to produce an alcohol.

If you are given the reagent to add to an alkene and asked for the product, just think what functional group can be added to the carbon chain from the reagent.

If you are given the product and asked for the reagent, just think how this product’s functional group differs from an alkene: what atoms are missing?

STOP AND CHECK:


The definition for an addition reaction. What kinds of molecules can take part in addition reactions. Other than a polymer, the possible organic molecules that can be produced

from alkene addition reactions. The possible reagents that can be used in alkene addition reactions.


Markovnikov’s RuleWhen an asymmetrical alkene (different number and/or type of atoms on either side of the double bond) is involved in an addition reaction there can be two different compounds produced. We call these the major and minor products, where the major product is produced in greater amounts. Two products are made because if the



hydrogen atom is placed on one of the carbons it produces a completely different molecule than if it was placed on the neighbouring carbon instead.

When it comes to addition reactions you need to use Markovnikov’s Rule

This rule states that the hydrogen atom is preferentially added to the carbon with the highest number of hydrogen atoms already attached.

To help you remember this rule, think “the rich get richer”.

Using the alkene to haloalkane reaction as an example, there can sometimes be two possible products formed:

There are two possibilities where the H and Cl atomscan be added

the H is added to the Carbon with the

least number of H atoms

already attached minor product major product

CH3 + HClCH

CH

H

CH3 CH

CH

H ClH CH3 C

HCH

Cl HH

CH3 + HClCH

CH

H

C... CH Cl C... C H Cl

The H is added tothe carbon with

the most H atoms already attached

1-chloropropane 2-chloropropane

Make sure you name both products, as you might find they are actually the same molecule (the same name). This is because only one product is formed in addition reactions involving symmetrical alkanes.

STOP AND CHECK:


What is meant by the phrase “the rich get richer”, in terms of addition reactions. What is the difference between the major and minor product.


Elimination ReactionsIn elimination reactions, atoms are removed from two neighbouring carbon atoms in the main chain

Once this has been done, the carbon atoms have a bit of a problem: they no longer have full valence shells, as they no longer have four bonds formed.



When atoms are removed, Carbon atoms need to bond with one another and form double (or even triple) bonds.

e.g. CH3 CH2 CH2 CH2

H and Cl atoms are removedfrom the molecule

a double bond is formed instead

the carbon atoms no longer have full valence shells

Clheat

KOH(alc)+ HCl+

H CH

CH

H ClCl H C

Cl

H

+ H

CH

ClC

Cl

H

H

H

H+ H

C

Elimination reactions are the opposite of addition reactions...

...so it would seem logical that if alkenes are the reactants in all addition reactions, then alkenes are the products in all elimination reactions. That’s because elimination reactions involve the formation of a double bond after the removal of atoms or functional groups from two neighbouring carbon atoms.

Alkenes can be made from two types of organic molecules: alcohols and haloalkanes.

Reaction 1: Alcohol to Alkene

Remember that to produce an alcohol from an alkene in an addition reaction, acidified water was added to provide the hydrogen atom and hydroxyl group needed.

To go backwards, and convert an alcohol to an alkene, a hydrogen atom and a hydroxyl group need to be removed so that the double bond can be reformed

When you are thirsty, you are dehydrated because you don’t have enough water. In chemistry, there are certain substances that act as dehydrating agents that remove water.

One of these is concentrated sulfuric acid (H2SO4) and can be use to remove the equivalent of a water molecule (H + OH) in the elimination reaction, converting an alcohol to an alkene. Once the hydrogen atom and hydroxyl group are removed from the alcohol they combine to form water. The carbon atoms they were originally bonded to need to refill their valence shells, so instead form a double bond with one another.

Using ethanol as an example, the overall reaction looks like: conc. H2SO4

CH3 - CH2 - OH → CH2 = CH2



In the addition of acidified water to alkenes, we were worried about which carbon atom to add the hydrogen to and which one to add the hydroxyl group to. There is only one carbon that will have the hydroxyl group (-OH) attached, but when there are carbon atoms on either side, there will be two possible options to remove the hydrogen atom from. This influences where in the chain the double bond forms, and therefore influences the particular alkene produced.

OPTION 1

remove hydrogenfrom carbon 1

but - 1 - ene but - 2 - ene

H HCH

HCH

OHCH

HCH

H

H HC

H

HC

H

OHC

H

HC

H

HH HC

H

HC

H

OHC

H

HC

H

H

OPTION 2


HCH

CH

CH

HHCH

HH HC

H

HCH

CH

CH

H

A similar rule to Markovnikov’s Rule - “Reverse Markovnikov’s” rule (also sometimes called Saytseff’s rule) - is used to determine which product is most likely to form (and therefore be formed in greater amounts). For now, just become familiar with how the reaction works - and we’ll cover this rule after “Elimination Reactions”.

Reaction 2: Haloalkane to Alkene

Remember that to produce a haloalkane from an alkene in an addition reaction, either HCl or HBr was added to provide the hydrogen atom and halogen needed.

To go backwards, and convert a haloalkane to an alkene, a hydrogen atom and the halogen (either Cl or Br) need to be removed so that the double bond can be reformed

Unfortunately, it’s not obvious what the reagent will be: alcoholic potassium hydroxide (KOH(alc)) is used.

Be very careful of the state of this reagent. It isn’t any old potassium hydroxide, and especially isn’t aqueous potassium hydroxide, it is potassium hydroxide dissolved



in alcohol, producing alcoholic potassium hydroxide. This is shown using the “alc” symbol: KOH(alc).

Aqueous potassium hydroxide (KOH(aq)) is a similar reagent but is used later on in a different organic reaction.

When the hydrogen and halogen atom are removed from the haloalkane they combine to form either hydrogen chloride (HCl) or hydrogen bromide (HBr), depending on the halogen atom.

Using bromoethane and chloroethane as examples, the overall reaction will look like either:

KOH(alc)

CH3 - CH2 - Br → CH2 = CH2 + HBr

KOH(alc)

CH3 - CH2 - Cl → CH2 = CH2 + HCl Just like with the elimination reaction involving alcohols, there’s the issue of which carbon atom to remove the hydrogen from

A similar rule to Markovnikov’s Rule - “Reverse Markovnikov’s Rule” - is used to determine which product is most likely to form (and therefore be formed in greater amounts). This will be covered after “Elimination Reactions”.

Summary

All elimination reactions produce alkene molecules. They are elimination reactions because the double bond is formed after atoms or functional groups are removed from neighbouring carbon atoms. These removed atoms or functional groups combine to produce side products.

The following reagents can be used to produce alkenes in elimination reactions:

1. H2SO4 is a dehydrating agent used to convert alcohols to alkenes. 2. KOH(alc) is used to convert haloalkanes to alkenes.

STOP AND CHECK:


The definition for an elimination reaction. What kinds of molecules can take part in elimination reactions.



The product of all elimination reactions. The reagents used and side products formed in the elimination of alcohol

and haloalkanes.


Reverse Markovnikov’s Rule

When it comes to elimination reactions we sometimes need to use what is referred to as “Reverse Markovnikov’s Rule”.

For some elimination reactions involving alkanes there are two possible pairs of carbon atoms where the double bond can form between

Say we remove a functional group from the 2nd carbon, we can either remove the hydrogen from the 1st carbon or from the 3rd carbon. This influences where the double bond will be formed and therefore influences what product is made!

OPTION 1


but - 1 - ene but - 2 - ene

H HCH

HCH

OHCH

HCH

H

H HC

H

HC

H

OHC

H

HC

H

HH HC

H

HC

H

OHC

H

HC

H

H

OPTION 2


HCH

CH

CH

HHCH

HH HC

H

HCH

CH

CH

H

Here, the major product is the one where the hydrogen atom is removed from the carbon with the least number of hydrogen atoms already attached.

To help you remember this rule, think “the poor get poorer”.

There are two times when you will use Reverse Markovnikov’s Rule:

1. Alcohol to alkene2. Haloalkane to alkene



STOP AND CHECK:


The two times when you will need to use Reverse Markovnikov’s Rule. What is meant by the phrase “the poor get poorer”, in terms of elimination

reactions. What is the difference between the major and minor product.


Oxidation Reactions

Oxidation can be thought of as gaining oxygen bonds

If you did the Level 2 Chemistry Redox internal you had another definition for oxidation. But, for this topic we can keep it as simple as gaining oxygen bonds.

So, if oxygen atoms are added to the molecule, that molecule has been oxidised.

There are two main types of organic molecules which undergo oxidation:

Reaction 1: Oxidation of Primary Alcohols

Alcohols can be oxidised. If we think about the fact that oxidation involves the addition of oxygen atoms, we can work out what the result of oxidation or an alcohol would be. Which functional group has more oxygen atoms than alcohols? Carboxylic acids!

However, not all alcohol molecules can be oxidised

Remember the carboxyl group can only be found at the end of a carbon chain. Therefore, only alcohols with the hydroxyl group on the 1st carbon atom can be oxidised to carboxylic acids.

Thinking back to that time we learnt about the difference between primary, secondary and tertiary alcohols gives us some language to use here.

If we think about these classifications, remember that that oxidation of primary alcohols produces a carboxylic acid, but tertiary alcohols cannot be oxidised.

Secondary alcohol molecules can be oxidised to a different kind of organic molecule that is covered in Level 3 Chemistry. Therefore, don’t worry about oxidation of secondary alcohol molecules in Level 2 Chemistry.



In order to oxidise a primary alcohol, an oxidising agent must be added

There are two possible reagents:

1. Acidified permanganate solution (H+/MnO4-)

2. Acidified dichromate solution (H+/Cr2O72-)

These oxidation reactions are associated with colour changes

Acidified permanganate solution is purple. When it oxidises a primary alcohol it the permanganate is converted into manganese ions (Mn2+), which forms either a colourless solution, or a very pale pink solution. Acidified dichromate solution is orange. When it oxidises a primary alcohol it then dichromate is converted into chromium ions (Cr3+), which form a green solution.

Using ethanol as an example, the oxidation of primary alcohols looks like:

H+/MnO4- or H+/Cr2O7

2-

CH3-CH2-OH → CH3-COOH

Reaction 2: Oxidation of Alkenes

Alkenes can also undergo oxidation to form diols

Diols are molecules with two hydroxyl (-OH) groups.

Again, an oxidising agent needs to be used

Just like with primary alcohols, acidified permanganate solution (H+/MnO4-) can be

added. However, acidified dichromate (H+/Cr2O72-) cannot be used.

Using ethene as an example, the oxidation of alkenes looks like:

H+/MnO4-

CH2 = CH2 → CH2 (OH) - CH2 (OH)

STOP AND CHECK:


What happens in an oxidation reaction. The two types of organic compounds can undergo oxidation reactions. The two oxidising agents you need to know in Level 2 Chemistry.




Substitution Reactions

In substitution reactions, there’s a tag team going on. Atoms leave the molecule and get a mate to jump in and take their place.

e.g. CH3 - CH2 - Cl + KOH(aq)

the Cl atom is removed ... and it is replaced by an OH group

CH3 - CH2 - Cl + KOH

heatCH3 - CH2 - OH + KCl

CH3 - CH2 - + K - OH

CH3 - CH2 - OH + K - Cl

Cl

When looking at substitution reactions, it is important to ask yourself what is being taken away and what is being put in its place

Since C-C and C-H bonds do pretty much nothing, we will always be swapping the interesting looking bits: halogen atoms (F, Cl, I, Br), hydroxyl groups (-OH) and amine groups (-NH2).

After that we can look at the reagent (the thing we add to our organic molecule) and see what might go in its place. These are often things like halogen atoms, hydroxyl groups or amine groups; for example, the -OH from the KOH reagent.

There are 4 substitution reactions, each involving either halogen atoms (haloalkanes), hydroxyl groups (alcohols) and amine groups (amines). Haloalkanes can be converted to alcohols and amines, alcohols can be converted to haloalkanes, and alkanes can be converted to haloalkanes.

Reaction 1: Haloalkane to Alcohol

To convert a haloalkane to an alcohol, the halogen atom needs to be removed and a hydroxyl group needs to be put in its place. The reagent that is added to the haloalkane is aqueous potassium hydroxide (KOH(aq)).

Remember, we came across alcoholic potassium hydroxide before. They are not the same reagent, and alcoholic potassium hydroxide (rather than aqueous) is used in the elimination reaction, converting haloalkanes to alkenes.

The KOH splits apart, the halogen comes off the carbon it is bonded to, the K and halogen combine to form potassium chloride or potassium bromide (depending on the halogen), and the OH group bonds to the same carbon atom.



Using chloroethane and bromoethane as the two examples, the overall reaction will look like either:

CH3- CH2- Cl + KOH(aq) → CH3- CH2- OH + KClCH3- CH2- Br + KOH(aq) → CH3- CH2- OH + KBr

Reaction 2: Haloalkane to Amine

Instead of adding alcoholic potassium hydroxide to the haloalkane, we can add concentrated ammonia (NH3). What functional group contains a nitrogen atom? Amines! When concentrated ammonia is added to a haloalkane, the halogen comes off the carbon and combines with one of the hydrogens in ammonia to form a hydrogen halide (either hydrogen chloride or hydrogen bromide), and the leftover -NH2 bonds do the same to carbon to form the amine.

You may have noticed that I keep calling the reagent “concentrated ammonia”. The fact that the ammonia is concentrated is super duper important! So don’t forget to add that in.

Using chloroethane and bromoethane as the two examples, the overall reaction will look like either:

CH3- CH2- Cl + conc. NH3 → CH3- CH2- NH2 + HCl CH3- CH2- Br + conc. NH3 → CH3- CH2- NH2 + HBr

Reaction 3: Alcohol to Haloalkane

We’ve already seen alcohols being formed from haloalkanes with alcoholic KOH. Going backwards requires the removal of the hydroxyl (-OH) group and the addition of a halogen. In Level 2 Chemistry we are only interested in producing a chloroalkane, rather than a bromoalkane.

There are actually a handful of possible reagents that could be used - PCl3, PCl5 or SOCl2

Using ethanol as an example, the overall reaction with each of the possible reagents looks likes:

1. CH3-CH2-OH + SOCl2 → CH3-CH2-Cl (+ SO2 + HCl)2. 3CH3-CH2-OH + PCl3 → 3CH3-CH2-Cl (+ H3PO3)3. CH3-CH2-OH + PCl5 → CH3-CH2-Cl (+ HCl + POCl3)

A lot is going on in this reaction, but simply one of the Cl atoms from SOCl2, PCl3 or PCl5 is going to be involved in the substitution, and when the -OH group comes off



the carbon chain it jumps in its place. You don’t need to worry about the non-organic products that are in brackets - they’re just there to balance the equations.

Reaction 4: Alkane to Haloalkane

The last substitution reaction involves alkanes being converted into haloalkanes. Here, one hydrogen atom is removed from the alkane and is replaced with one halogen atom: either chlorine from Cl2 or bromine from Br2. The hydrogen that is removed combines with the remaining Cl or Br atom to form a hydrogen halide (either hydrogen chloride or hydrogen bromide).

However, you can’t just add chlorine or bromine and hope for the best. The reaction requires ultraviolet light (UV light) to go ahead. The reason for this is that alkanes are not very reactive. So, UV light gives that extra boost of energy to get the reaction going.

Using ethane as an example, the overall reaction will look like either:

UV light

CH3- CH3 + Cl2 → CH3- CH2- Cl + HCl

UV light

CH3- CH3 + Br2 → CH3- CH2- Br + HBr

STOP AND CHECK:


The definition for a substitution reaction. The possible kinds of functional groups that may be swapped in a substitution

reaction.


Neutralisation Reactions with Carboxylic Acids

Time for a cheeky throwback to Level 1 Science. Think way back to the Acids and Bases external.

Remember that, a reaction between an acid and a base is known as a neutralisation reaction. It is called this, because when an acid reacts with a base, the products we end up with are neither acidic nor basic: they are neutral!

In general, all neutralisation reactions follow this simple format:



How neutralisation reactions go:

Acid + base salt + water

A salt is a neutral ionic compound.

When writing a reaction, we can begin by filling in the left hand side, which is where the acid and base go, as well as part of the right hand side - where we know water will always end up. We then use the parts of the acids and bases that don’t react into water to make up our salt.

But hold up.

Just like any other acid, Carboxylic acids can be involved in neutralisation reactions. Here are some examples:

1. Carboxylic acid + water: CH3COOH(aq) + H2O(l) ⇌ CH3COO-(aq) + H3O

+(aq)

2. Carboxylic acid + metal carbonate: 2CH3COOH(aq) + Na2CO3(aq) → 2CH3COONa(aq) + H2O(l) + CO2(g)

3. Carboxylic acid + base: CH3COOH(aq) + NH3(aq) → CH3COO-(aq) + NH4

+(aq)

The key to remember here, is that every time the Carboxylic acid reacts, it loses a Hydrogen to form an ion or salt on the product side.

water

donates proton

propanoic acid

+

-+

CH3 CH2 CO O

H HO H

OH

H

Hpropanoate acid hydronium ion

+CH3 CH2 CO

O

STOP AND CHECK:

Turn your book over and see if you can remember the main carboxylic acid reactions using a different carboxylic acid molecule as an example.

Acid-Base Reactions involving Amines

There are 2 main acid-base reactions involving amines, which are similar to some of the carboxylic acid reactions:



1. Amine + water: CH3CH2NH2(aq) + H2O(l) ⇌ CH3CH2NH3+

(aq) + OH-(aq)

2. Amine + acid: CH3CH2NH2(aq) + HCl(aq) → CH3CH2NH3+

(aq) + Cl-(aq)

When a base reacts with water, water acts as an acid to complement it. Here, water donates a proton to the amine, leaving hydroxide (OH-) ions in solution. As the hydrogen ion (proton) joins onto the amine group, we say the amine is protonated.

In reactions with acids, the amine gains a hydrogen ion (proton) from the acid, leaving a protonated amine and a spare ion from the acid.

wateramine accepts proton

hydroxide

propanamine

+

-+

CH3 CH2 CH2

H OH HH

N

+CH3 CH2 CH2

H

HN O HH

STOP AND CHECK:

Turn your book over and see if you can remember the 2 main amine reactions using a different amine molecule as an example.

Quick QuestionsA good way of bringing together all of the organic reactions is to prepare a reaction flowchart that shows how to get one from functional group to another. Creating one of these helps to see the ‘bigger picture’ of the Organic Chemistry topic. Use the template below to create your own:

reaction type:

reaction type:reaction type:

reaction type:

reaction type:reaction type:

reaction type:

reaction type:

reaction type:

reaction type:

?

AMINE

HALOALKANE

?DI - HALOALKANE

? ?

? ?

?

?

??

ALKENE

CARBOXYLIC ACID

ALCOHOLALKENE

DIOL

?



Fill in the circles with the correct reagent and conditions required for the reaction to occur.

Make sure you classify each reaction as either an addition, elimination, substitution or oxidation reaction.

POLYMERSAlkenes can undergo a special kind of addition reaction called a polymerisation reaction. Here, the alkene molecule is joined together with heaps and heaps of identical alkene molecules - forming a massive chain.

The double bond between two carbon atoms in the alkene is broken which frees up two covalent bonds, allowing the carbon atoms at the end of the alkene to each bond with the ends of another alkene, and so on.

To keep it nice and simple, all you need to know is:

How these polymers are formed from small alkenes.How to go about naming these polymers. What polymers actually are!

Polymerisation Reaction

Polymerisation reactions are just a series of addition reactions.

For a polymerisation reaction to occur, there needs to be high pressure, high temperature, and the addition of a catalyst.

When we talk about polymerisation reactions, we refer to the long chain that has been built as the ‘polymer’, and the alkene molecules we started with as the ‘monomers’.

When it comes to naming the polymers formed, it is generally as easy as chucking “poly-“ at the start of the monomer’s name.

To draw out the polymerisation of an alkene, the key is to rearrange the structural formula so that the two carbons in the double bond are placed in the centre. The rest of the alkene molecule is considered as distinct groups coming off each of these two carbon atoms.



ethene ethene monomer

and so on... polymer (polyethene)

addition

CH

HCH

HCH

HCH

H

moreaddition

+

+

CH

HCH

HCH

HCH

H

CH

HCH

HCH

HCH

H

CH

HCH

HCH

HCH

H

CH

HCH

HCH

HCH

HCH

HCH

HCH

HCH

H

Let’s try a more difficult polymer, using something like 1-chloroprop-1-ene as our monomer. The first thing to do is to redraw your monomer so that you put the double bond in the middle. It should look like two carbon atoms each with two groups coming off it.

In 1-chloroprop-1-ene we have more than 2 carbon atoms. This is okay, you simply put one of the carbons as a side group as shown in the diagram below.

The same principal applies: the double bond is broken which frees up an available bond so that monomers can be joined together endlessly.

1-chloroprop-1-ene1 - chloroprop - 1 - ene

redrawn monomer

poly-1-chloroprop-1-enepolymer

CCl

H HCH

CH

CH3

CCl

HCH

H

CH3

C CH

H

Cl

CH3

C CH

H

Cl

CH3

C CH

H

Cl

CH3

C CH

H

Cl

CH3

C CH

H

Cl

CH3

C CH

H

Cl

CH3

C CH

H

Cl

CCl

H

H

CH3

C

addition

addition

+

+

CH3

C CH

H

Cl

CH3

C CH

H

Cl

CH3

C CH

H

Cl

A polymer can therefore be described as a very large molecule composed of repeating units

These repeating units are smaller molecules called monomers, which must be joined together to form this continuous polymer.



STOP AND CHECK:


What are monomers and polymers. The conditions needed for the polymerisation reaction to occur. How to name polymers.


Quick QuestionsWhat are polymers and how are they formed?

PROPERTIES OF ORGANIC COMPOUNDSWaaaaay back at the start of the Walkthrough Guide, we said that functional groups are super duper important because they affect the chemical and physical properties of the compound. Now that you should be familiar with the main functional groups out there, we can now link structure with function.

First we’ll revisit the idea of polarity - covered in more depth in Structure and Bonding - and use this to classify our organic molecules as polar or non-polar. Next, we’ll think about what affects melting and boiling point, and use the structure of our organic molecules to explain which ones melt or boil at the highest temperatures. Finally, we’ll look at the idea of solubility and use the general rule “like dissolves in like” to explain which of our organic molecules will dissolve in water and which ones won’t.

Introduction to Polarity

Polarity is important in Organic Chemistry as it can tell us a lot about the properties of a molecule, from whether it will dissolve in water, to the temperature at which it boils.

But, what is polarity?

?



Arctic (North Pole)

magnet

Antarctica (South Pole)

S

Npolarity

On opposite ends of the planet, Earth has a North and South pole. If have a look at magnets, we call one end the north pole and the other end the south pole. Because of this, both the Earth and magnets are said to be polar, or have polarity.

Chemical bonds and molecules can also be polar (or non-polar).

Here, polarity just means the “separation of charge”.

Polar molecules will have a positively-charged region and a negatively-charged region, while non-polar molecules will have no real charge difference across the molecule. In a polar covalent bond, one of the atoms ends up with a partial positive charge while the other a partial negative charge. In a non-polar covalent bond, there is no difference in charge.

To help us understand whether molecules are polar or non-polar we need to talk about something called, “electronegativity”.

All atoms are attracted to bonding electrons, but some are more attracted to them than others

The stronger their feelings for these electrons, the stronger the attraction, and the tighter the atom will hold onto electrons in a covalent bond. This is electronegativity.

Electronegativity describes the tendency of an atom to attract bonding electrons

So, how do you know which atoms are more attracted to bonding electrons than others?

If you go down a group in the Periodic Table the electronegativity decreases, but if you go across a period (from left to right), the electronegativity increases.

This means that the least electronegative atoms are cesium and francium, whereas the most electronegative atoms are nitrogen, oxygen and fluorine. (We ignore the Noble Gases since they are unreactive).



Let’s grab two identical non-metal atoms, say two hydrogen atoms

They both have 1 valence electron but need 2 in total to be stable. Sharing them sounds like a great idea at this point!

Even though they want to share, both hydrogen atoms secretly want the electrons to themselves. So, there is a bit of tug of war going on. But, because both atoms are the same they pull on these bonding electrons with the same amount of strength. This means that bonding electrons will happily zip around the nucleus of both hydrogen atoms, spending the same amount of time around each one.

This means there is no real difference in charge between these two atoms, so their covalent bond is non-polar.

symmetrical electrondistribution

H He

e

What happens when we get two different non-metal atoms, say, a hydrogen atom and a chlorine atom?

Chlorine has 7 valence electrons but needs 8, while hydrogen has 1 but needs 2. So, they both decide to share 1 electron.

Since chlorine is more electronegative than hydrogen, chlorine has a larger tendency to attract the bonding electrons; bonding electrons are attracted more to the chlorine than they are to the hydrogen. Although the 2 bonding electrons are shared, chlorine pulls more tightly on them. We end up with the bonding electrons spending more time around chlorine nucleus than with hydrogen.

Partial Charges:

Since chlorine isn’t being fair and is being greedy instead (and because electrons are negatively charged), it ends up with a partial negative charge, which is represented by the “delta negative” symbol (δ-).

To give hydrogen something to be happy about, it ends up with a partial positive charge, which is represented by the “delta positive” symbol (δ+).

This kind of covalent bond is polar



That’s because there is a separation of electrical charge. Since it is polar it creates what is called a, “dipole”, which is the separation of electrical charge that we just talked about.

uneven electrondistribution

partial negativechargepartial positive

chargeH Cl

e

eδ+ δ -

As a general rule in Organic Chemistry:

If there are no highly electronegative atoms, like oxygen or nitrogen atoms, attached to the main carbon chain the molecule will likely be non-polar. If there are oxygen or nitrogen atoms in the functional group, then the molecule is likely to be polar.

STOP AND CHECK:


The definition of polarity when it comes to chemistry. How polarity can be applied to molecules and covalent bonds. What electronegativity is. Which atoms have higher electronegativity values, and which ones have lower

values. What are the requirements to make a non-polar covalent bond in terms of the

atoms – are they the same or different atoms? Why non-polar covalent bonds have no separation of charge. What are the requirements to make a polar covalent bond? Why polar covalent bonds have a separation of charge.


Polarity of Organic CompoundsIf we consider the organic compounds containing just carbon and hydrogen atoms - alkanes, alkenes and alkynes - we can say that they are always non-polar no matter how long the carbon chain is.



Alkane, alkene and alkyne molecules have a symmetrical shape which makes them non-polar molecules.

Haloalkanes are also considered non-polar

If you’ve had a look at Structure and Bonding already you hopefully remember that halogens are quite electronegative – more so than carbon and hydrogen. This would lead anyone to believe that haloalkanes are polar due to this negatively-charged region.

The halogen can scream negative all it likes, but the non-polar carbon chain drowns out the noise from the halogen, making the molecule non-polar overall - it doesn’t take much to be drowned out. The addition of a halogen atom was a nice touch, but it’s not drastic enough to make haloalkanes that much more exciting than alkanes.

CHH

HH CH

H

HCl

alkane halo - alkane

This means they essentially just have the same properties as alkanes, alkenes and alkynes.

Compounds containing oxygen or nitrogen atoms are usually polar overall

Oxygen and nitrogen are very electronegative atoms - more so than carbon and hydrogen atoms. This means when you’ve got one of these atoms attached to the main carbon chain there is a region of negative charge, giving the molecule polarity.

Alcohols, amines and carboxylic acids contain these atoms. Alcohols have the hydroxyl group (OH-) composed of an oxygen atom bonded to a hydrogen, amines have the amine group composed of a nitrogen atom bonded to two hydrogen atoms (NH2), and carboxylic acids have the carboxyl group (-COOH) composed of a carbon atom bonded to an oxygen atom via a double bond and also to a hydroxyl group.

ethanol

hydroxyl group

CH3 CH2 OH

ethanamine

amine group

CH3 CH2 NH2

ethanoic acid

carboxyl group

CH3 CO

OH



Therefore, it would be reasonable to think that alcohols, amines and carboxylic acids are polar molecules.

Only small alcohols, amines and carboxylic acids are polar

When these organic molecules are small - generally less than 5 carbon atoms - the polar functional group takes up a large enough proportion to make the molecule polar overall.

As more carbon atoms are added to the main carbon chain, the polar functional groups take up a smaller and smaller proportion of the molecule. They are essentially silenced by the large non-polar carbon chain. This means that large molecules - with more than 5 carbon atoms - are generally considered to be non-polar.

ethanol octanol

= polar

CH3 CH2 OH

= essentially non-polar

CH3 CH2 CH2 CH2 CH2 CH2 CH2 OH

In an exam situation you will either be given a really short chain or a really long chain, and so the distinction of whether they are going to be polar or non-polar will be much easier.

STOP AND CHECK:


Why alkanes, alkenes and alkynes are non-polar. Whether haloalkanes are polar or non-polar. Which organic molecules are considered polar - are they always polar?


Introduction to Melting/Boiling Point

All substances can exist as gases, liquids and solids at different temperatures and pressures

For example, water molecules exist as a solid (ice) at temperatures below 0°C. As we turn up the dial and get things heated up, the ice melts and forms liquid water. If we want to take things to the next level, we can boil the water up to 100°C and produce a gaseous form of water (steam).



Melting and boiling

When the temperature increases, the amount of heat energy increases

This is used to break any bonds holding the solid or liquid together.

As a general rule, the stronger the force of attraction the more heat energy is required to break it. (We will get onto which forces are stronger than others in the next few sections but keep this in mind as we go through because it is really important). The melting point is the temperature at which solid melts into a liquid, while the boiling point tells us what temperature is needed to boil that liquid into a gas.

solid

intermolecular force

melting

liquid

gas

boiling

STOP AND CHECK:


How solids are converted to liquids and how liquids are converted to gases.


Melting/Boiling Point of Organic Compounds

Alkanes, alkenes, alkynes and haloalkanes have low melting and boiling points.

All of these molecules are non-polar and are held together by weak intermolecular forces. As these are weak forces, it doesn’t take much energy in the form of heat to break them, transforming a solid into a liquid, or liquid to gas, easily. This is why alkanes, alkenes, alkynes and haloalkanes are often gases at room temperature.

You don’t have to worry about comparing the melting/boiling points between alkanes, alkenes and alkynes as they are so similar, but haloalkanes will have slightly higher melting and boiling points. This is due to the halogen atom giving it slightly more polarity.



Alcohols, amines and carboxylic acids have higher melting and boiling points

Compared to alkanes, alkenes, alkynes and haloalkanes, these organic compounds have higher melting and boiling points when the carbon chains are the same length.

Because alcohols, amines and carboxylic acids are polar molecules, they are held together by stronger intermolecular forces than those between non-polar molecules. This is because there is an attraction between the positively-charged and negatively-charged regions of neighbouring molecules.

It’s not as important to compare the melting or boiling points of alcohols, amines and carboxylic acids - what’s important is that they are higher than the other, non-polar organic compounds. This explains why all alcohols are either liquid or solids at room temperature, similar with amines and carboxylic acids.

For all organic molecules the melting and boiling point increases as the carbon chain length increases

This is because the strength of intermolecular forces depends on the number of electrons, and as the molecular mass increases the number of electrons also increases. This leads to stronger attractive forces between molecules, meaning more heat is required to break the bonds.

Carbon atoms in a straight chain have higher melting/boiling points than branched chains

Although, not so important in Level 2 Chemistry it is good to be aware that organic compounds containing branched chains have lower melting/boiling points.

The exact reason is covered more in Level 3 Chemistry, but basically, when all the carbon atoms are in a straight chain these intermolecular forces can do their job more easily, leading to stronger attractive forces.

STOP AND CHECK:


The name of the attractive force that holds molecules together. Why alcohols have higher melting/boiling points than alkanes, alkenes,

alkynes and haloalkanes of similar lengths. The trend in melting/boiling point of organic molecules when the carbon chain

increases.



Introduction to Solubility

Solubility tells us how likely something is to dissolve in something else. If a compound is soluble in water it will dissolve when added.

The golden rule of solubility is that “like dissolves in like”

So, polar molecules dissolve in water, which is a polar liquid, but not in non-polar liquids.

On the other hand, non-polar molecules dissolve in other non-polar liquids but not in water. You will always be told if a solvent is non-polar. For example, it might say something like “hexane, a non-polar solvent…”

The thing that gets dissolved in the liquid is called the “solute”, while the liquid it dissolves in, such as water, is called the “solvent”.

molecule

water molecule

solid

intermolecule force

a solution

bonding with water

O

O

O

O

H

H

H

H

H

H

H

H

O

H

H

dissolving

STOP AND CHECK:


What solubility means, and the rules that determine if something is soluble in something else.


Solubility of Organic CompoundsThe solubility of organic compounds comes back to the idea that “like dissolves in like”. In Level 2 Organic Chemistry we are interested in dissolving these organic compounds in water.



Do alkanes, alkenes, alkynes and haloalkanes dissolve in water? Nope!

That would be too much fun for them. The reason is that they are all non-polar molecules due to being symmetrical. Because we know that “like dissolves in like”, we know that these non-polar molecules are insoluble in polar liquids, like water.

Instead, they don’t mix, and instead form separate layers. If you wanted to show you off, you could say that alkanes/alkenes/alkynes/haloalkanes and water are immiscible.

water

nomixing

alkane

Some alcohols, amines and carboxylic acids are soluble in water

Pour a bit of alcohol, amine or carboxylic acid into some water and POOF! It’s gone. It dissolves in the water because “like dissolves like”, and polar molecules are soluble in polar liquids, like water. This only works for small molecules, like those with between 1 and 4 carbon atoms in their main chain.

As we stretched out the molecule to 5 or more carbon atoms they begin to resist. Rather than mixing and mingling with the water molecules, the alcohol, amine or carboxylic acid sulks in the corner and instead forms a separate layer on top. Again, you will either be given a molecule with a really short chain or a really long chain, and so the distinction of whether they will be soluble or insoluble will be easy.

That’s because the bigger the molecule the less polar it becomes, as the polar part of the molecule (-OH for alcohols, -NH2 for amines and -COOH for carboxylic acids) is drowned out by the longer non-polar carbon chain. So, these large molecules are insoluble in water.

STOP AND CHECK:


Why alkanes, alkenes and alkynes are insoluble in water. What will happen when you mix a haloalkane with water. Why small carboxylic acids and amines are soluble in water but large alcohols

are insoluble in water.




Quick Questions Explain the properties of alkanes, alkenes and alkynes, and any differences between them.

Discuss the properties of haloalkanes based on their functional group. Discuss the properties of alcohols (and diols) based on their functional group. Discuss the properties of carboxylic acids based on their functional group. Discuss the properties of amines based on their functional group. Compare the properties of polar organic molecules with non-polar ones, giving reasons for any differences.

IDENTIFICATION TESTSPretty much all of the organic compounds are colourless, which is both boring and dangerous. Who knows, maybe you pick up the wrong colourless solution and blow up the lab… Therefore, there needs to be a way to quickly make sure you’ve got the right compound, which is where identification tests come in.

So, what do you need to know to prevent a chemical explosion:

How to use red and blue litmus paper to tell if something is acidic, basic or neutralHow to separate primary alcohols from tertiary alcohols using dichromate or permanganate solution How to use bromine water to tell if you’re dealing with alkanes or alkenes

Red and Blue Litmus Paper

It’s time to have a look at litmus paper. These bad boys of junior science are used to determine whether a solution is acidic, basic or neutral.

Litmus paper comes in two flavours: red and blue

If we throw some blue litmus paper into a basic solution, nothing happens. But, add it to an acidic solution and BAM! It goes through a transformation and comes out totally red. The opposite happens with red litmus paper. It stays true to itself in acidic solution, but goes blue when soaked in basic solution.

This means that carboxylic acids, our organic acids, will turn blue litmus paper red and amines, our organic bases, will turn red litmus paper blue.

?



Let’s not forget about neutral solutions, like alcohols, haloalkanes, alkanes, alkenes and alkynes. Red litmus paper stays red and blue litmus paper stays blue in neutral solutions.

base

acid

neutral

base

acid

neutral

STOP AND CHECK:


What colour red and blue litmus paper will turn in the presence of an acidic solution. What colour red and blue litmus paper will turn in the presence of a basic solution. What colour red and blue litmus paper will turn in the presence of a neutral solution.


Dichromate or Permanganate Solution

Remember, primary alcohols can be oxidised to carboxylic acids, but tertiary alcohols just can’t be bothered. They’ve got the side chain on the same carbon as the hydroxyl group, and they’re not going to go to all the effort of removing that side chain just to add another oxygen atom.

The difference in their reactivity actually comes in handy as it allows us to distinguish primary alcohols from the rest

In order to oxidise primary alcohols, strong oxidants must be added.

The two most common reagents are acidified dichromate solution (H+/Cr2O72-) and

acidified permanganate solution (H+/MnO4-). To tell whether an alcohol has been

oxidised, a colour change will be observed:



Orange acidified dichromate solution will be reduced to green chromium ions (Cr3+).

primary alcohol

Cr2O72-

tertiary alcohol

Cr2O72-

Cr3+

Cr2O72-

Purple acidified permanganate solution will be reduced to colourless (or pale pink) manganese ions (Mn2+).

primary alcohol

AND

MnO4- Mn2+ MnO4

-

tetriary alcohol

MnO4-

STOP AND CHECK:


What is formed when primary alcohols are oxidised. The colour change that occurs when dichromate solution is added to a

primary alcohol and to a secondary or tertiary alcohol. What is formed when dichromate reacts with a primary alcohol. The colour change that occurs when permanganate solution is added to a

primary alcohol and to a secondary or tertiary alcohol. What is formed when permanganate reacts with a primary alcohol. Why dichromate and permanganate don’t react with secondary or tertiary

alcohols.




Bromine water

Bromine Water

Alkanes and alkenes are annoyingly similar, as they both contain just carbon and hydrogen atoms. It’s a bit like seeing a cookie which looks it could be chocolate chip or raisin. Thankfully we have bromine water, a orange-brown solution, to solve the mystery.

Both alkanes and alkenes undergo a reaction with bromine water to form a bromoalkane (a haloalkane)

But, alkanes and alkenes are a little bit different in how they react.

Alkenes react straightaway, via an addition reaction, with no worries at all.

Alkanes, however, need a bit of help from UV light. And even then, the reaction is quite slow.

When bromine water reacts, the solution loses its colour as the colourless bromoalkane forms

So, to solve the mystery of the unknown solution, add bromine water without UV light and see whether the yellow-brown colour disappears.

alkene

Br2 CH3-CH2-CH2-CH2-CH2-CH(Br)-CH2-Br

+CH3-CH2-CH2-CH2-CH2-CH=CH2

alkane

Br2 Br2

+CH3-CH2-CH2-CH2-CH2-CH2-CH3 +CH3-CH2-CH2-CH2-CH2-CH2-CH3



STOP AND CHECK:


What happens to bromine water when added to:• An alkene • An alkane without UV light.


Quick Questions How can litmus paper be used to distinguish between ethanoic acid, ethanamine (aminoethane) or ethanol?

How can an acidified permanganate solution be used to distinguish between propanol and 2-methylpropan-2-ol?

How can bromine water be used to distinguish octane from oct-1-ene?

In the lab, there are 5 beakers containing: ethanol, ethanoic acid, ethanamine, hexane and hex-1-ene. However, there are no labels. Using just water, litmus paper and bromine water, how can each solution be identified?

?



KEY TERMSAddition Reaction:

A reaction involving the breaking of a double (or triple) bond, and the addition of new atoms or atom groups to the organic compound.

Branched Chain Isomer:Structural isomers which differ in the composition of the carbon backbone, due to the presence of branched groups attached to the main carbon chain (carbon backbone).

Elimination Reaction:A reaction involving the removal of atoms or atom groups from an organic compound, and the formation of a double bond between two carbon atoms in the compound.

Functional Group Isomers:Structural isomers that have different functional groups from one another (but are still composed of the same number and type of atoms).

Geometric Isomers:Isomers with the same molecular formula and structural formula, that differ in their arrangements of atoms in space around a double carbon-carbon covalent bond.

Markovnikov’s Rule:(For major/minor products of addition reactions) the hydrogen atom is added to the carbon with the most hydrogen atoms already attached. “The rich get richer”.

Polymer:A large molecule composed of small, repeating units, called monomers.

Positional Isomers:Structural isomers that differ in the position of their branched or functional groups. In other words, they differ in which carbon atoms their branched/functional groups are attached to.

Structural Isomer:Isomers with the same molecular formula but different structural formula. Structural isomers are also called constitutional isomers.

Substitution Reaction:An organic reaction involving the removal of one atom or a group of atoms (functional group) from an organic compound, and the addition of a new atom or group of atoms. In other words, it involves one group being swapped with another.

organic chemistry · 2019-07-18 · the different types of organic compound, making them different...

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