Organic Chemistry

Introduction

Alkanes

Nomenclature

Electron Dot structures

Li Be B C N O F

NeClass exercise 1:

Draw the electron dot structure of Carbon

Class exercise 2:

Draw the electron dot structure of oxygen and fluorine

Lewis Dot structures

Li Be B C N O F

Organic Chemistry

Chemistry of Carbon Bonding of H,O, X and N

Valence SummaryC H O N Halogen

Valence electrons

4 1 6 5 7

Valence 4 1 2 3 1

Bond types SingleDoubletriple

single Single Double

SingleDoubletriple

single

Complete Structural Formulas

Show the bonds between each of the atoms

H H

H C H H C H H H

CH4 , methane

H H Condensed Structural Formulas

H C C H CH3 CH3

H H Ethane

H H H

H C C C H CH3 CH2 CH3

H H H Propane

More Alkanes

IUPAC Names

Name # carbons Structural Formula

Methane 1 CH4

Ethane 2 CH3CH3

Propane 3 CH3CH2CH3

Butane 4 CH3CH2CH2CH3

Pentane 5 CH3CH2CH2CH2CH3

IUPAC NAMES

Name # carbons Structural Formula

Hexane 6 CH3CH2CH2CH2CH2CH3

Heptane 7 CH3CH2CH2CH2CH2CH2CH3

Octane 8 CH3CH2CH2CH2CH2CH2CH2CH3

Nonane 9 CH3 CH2 CH2CH2CH2CH2CH2CH2CH3

Decane 10 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3

Learning Check Alk1

A. What is the condensed formula for

H H H H

H C C C C H

H H H H

B. What is its molecular formula?

C. What is its name?

Solution Alk1

A. CH3CH2CH2CH3

B. C4H10

C. butane

Properties of Alkanes

So what exactly do these things do?

Physical Properties of Alkanes

1. Combustion - Alkanes are inflammable, i.e. they burn.

CH4 O2 CO2 OH2+ +2 2

2. Boiling and melting points a. Both bp and mp increase with increasing carbon number for straight-chain alkanes with formula CnH2n+2

Carbon Number Physical State C1- C4 gases C5 – C16 liquids C17 – C30 oils and greases C30 – C50 paraffin waxes >C50 plastics (polyethylene)

b. Branching tends to lower the boiling point and raise the melting point

BP 60oC 58oC 50oC

MP -154oC -135oC -98oC

Explanation:

MP Branching reduces the flexibility of the molecule which reduces the entropy term S in the equation Tmp = H/S. Since S is in the denominator, Tmp increases.

BP Branching reduces surface area (more compact structure), and therefore London dispersion forces which control boiling point for these molecules.

3. Solubility – alkanes are nonpolar molecules and therefore insoluble in water, which is polar. Alkanes are hydrophobic.

4. Densities – alkanes are less dense than water, with densities near 0.7 g/mL. Therefore they float on water, e.g. Exxon Valdez oil spill.

Naming Hydrocarbons (nomenclature)

Drawing Structures: It’s All Good

CH3

CH

CH

CH3

CH3

CH3

CH3

CHCH

CH3

2-butene

This is called the “condensed structure”

C C C C

H

H

H

H H H

H

H

CH3 CH CH CH3

On a test, choose a method that shows all HsCH3CH=CHCH3

Using brackets can also shorten some formulas: CH3CH2CH2CH2CH2CH3 vs. CH3(CH2)4CH3

Basic Naming of HydrocarbonsHydrocarbon names are based on: 1)type, 2) # of carbons, 3) side chain type and position

1) name will end in -ane, -ene, or -yne

2) the number of carbons is given by a “prefix” 1 meth- 2 eth- 3 prop- 4 but- 5 pent- 6 hex- 7 hept- 8 oct- 9 non- 10 dec-

Basic Naming of Hydrocarbons

Q - What names would be given to these:7C, 9C alkane2C, 4C alkyne6C, 3C alkene

heptane, nonaneethyne, butyneHexene, propene

Mnemonic for First Four Prefixes

First four prefixes Meth- Eth- Prop- But-

Monkeys

Eat

Peeled

Bananas

?Decade

Decimal

Decathalon

Other Prefixes

Pent-

Oct-

Dec-

Hex-, Hept-, Non-

Straight chain hydrocarbonsLearning Check

Pentane

Propane

Heptane

Ethane

Octane

Numbering Carbons

Q- draw penteneA- Where’s the double

bond? We # C atoms.

Naming compounds with multiple bonds is more complex than previously indicated.

When 2+ possibilities exist, #s are needed.Always give double bond the lowest number.Q - Name these

C C C CCH3

H

H

H

H H H

HCH31

C2

C3

C4

C5

H

H

H

H H H

HCH35

C4

C3

C2

C1

H

H

H

H H H

H

ethene

3-nonyne

2-buteneCH3

CH

CH

CH3

CH3 CH3

C2H4

1-pentene

Learning Check - Numbering Carbons

ethene

3-nonyne

2-buteneCH3

CH

CH

CH3

CH3 CH3

C2H4

Name the following compounds:

CH3 CH3

CH3

CH3Naming Side ChainsThe names of molecules with

branches are based on: side chains, root

The “root” or “parent chain” is usually the longest possible hydrocarbon chain.

The root must include multiple bonds if they are present. If a cyclic structure is present it will be the root even if it is not the longest chain.

Side chains are also called “side branches” or “alkyl groups”. Their names end in -yl.

Common side chains :-CH3 methyl, -CH2CH3 ethyl, -CH2CH2CH3 propyl

2,3-dimethylpentane

CH3 CH3

CH3

CH3

IUPAC Rules for Naming Hydrocarbons1. Choose the correct ending: -ane, -ene, or -yne2. Determine the longest carbon chain. Where a double

or triple bond is present, choose the longest chain that includes this bond. If there is a cyclic structure present, the longest chain starts and stops within the cyclic structure.

3. Assign numbers to each C of the parent chain. For alkenes and alkynes the first carbon of the multiple bond should have the smallest number. For alkanes the first branch (or first point of difference) should have the lowest #. Carbons in a multiple bond must be numbered consecutively.

4. Attach a prefix that corresponds to the number of carbons in the parent chain. Add cyclo- to the prefix if it is a cyclic structure.

5. Determine the correct name for each branch (“alkyl” groups include methyl, ethyl, propyl, etc.)

6. Attach the name of the branches alphabetically, along with their carbon position, to the front of the parent chain name. Separate numbers from letters with hyphens (e.g. 4-ethyl-2-methyldecane)

7. When two or more branches are identical, use prefixes (di-, tri-, etc.) (e.g. 2,4-dimethylhexane). Numbers are separated with commas. Prefixes are ignored when determining alphabetical order. (e.g. 2,3,5-trimethyl-4-propylheptane)

8. When identical groups are on the same carbon, repeat the number of this carbon in the name. (e.g. 2,2-dimethylhexane)

IUPAC Rules for Naming Hydrocarbons

ene

Naming Side ChainsExample: use the rules on this handout to

name the following structure

CH3 CH2 C

CH2

CH2 C

CH2

CH3

CH3

CH3

Rule 1: choose the correct ending

ene

Rule 2: determine the longest carbon chain

CH3 CH2 C

CH2

CH2 C

CH2

CH3

CH3

CH3

Naming Side Chains

Rule 3: Assign numbers to each carbon

CH3 CH2 C

CH2

CH2 C

CH2

CH3

CH3

CH3

ene

Naming Side Chains

Rule 3: Assign numbers to each carbon

CH3 CH2 C2

CH21

CH23

C4

CH25

CH3

CH3

CH36

CH3 CH2 C

CH2

CH2 C

CH2

CH3

CH3

CH3

ene

Naming Side Chains

1-hexene ene

Rule 4: attach prefix (according to # of Cs)

Naming Side Chains

CH3 CH2 C2

CH21

CH23

C4

CH25

CH3

CH3

CH36

CH3 CH2 C

CH2

CH2 C

CH2

CH3

CH3

CH3

CH3 CH2 C2

CH21

CH23

C4

CH25

CH3

CH3

CH36

Rule 5: Determine name for side chains

CH3 CH2 C

CH2

CH2 C

CH2

CH3

CH3

CH3

1-hexene 1-hexene

ethyl

methyl

methyl

Naming Side Chains

CH3 CH2 C

CH2

CH2 C

CH2

CH3

CH3

CH3

CH3 CH2 C2

CH21

CH23

C4

CH25

CH3

CH3

CH36

1-hexene2-ethyl-4-methyl-4-methyl-1-hexene

ethyl

methyl

methylRule 6: attach name of branches alphabetically

Naming Side Chains

Rule 7,8: group similar branches

CH3 CH2 C

CH2

CH2 C

CH2

CH3

CH3

CH3

CH3 CH2 C2

CH21

CH23

C4

CH25

CH3

CH3

CH36

1-hexene2-ethyl-4-methyl-4-methyl-1-hexene

ethyl

methyl

methyl

Naming Side Chains

Rule 7,8: group similar branches

CH3 CH2 C

CH2

CH2 C

CH2

CH3

CH3

CH3

CH3 CH2 C2

CH21

CH23

C4

CH25

CH3

CH3

CH36

2-ethyl-4,4-dimethyl-1-hexene

ethyl

methyl

methyl

Naming Side Chains

Similar questions will be issued on Moodle and in the tutorial sheets

2-butene

propene

1-butyne

Learning Check – Naming

CH3 CH CH2

CH3 CH CH CH3CH3 CH CH C

CH3 CH3

CH32,4-dimethyl-2-pentene

CH C CH2 CH3

b) same

c) 5-ethyl-4-methyl-2-heptyne

a) 3,3-dimethyl-1-pentene

CH2 CH C CH2 CH3

CH3

CH3

CH3 C CH CH2

CH3

CH2 CH3

CH CH CH2

CH2 CH3

CC

CH3CH3

CH3