naming alkanes 2/19/2016dr seemal jelani chem-1601

Naming Alkanes

05/04/23Dr Seemal Jelani Chem-160 1

1. Root name: name of longest continuous C chain (parent chain)• 2 equally long? Choose the one with more branches

2. Number C atoms in chain, starting at end with first branch


4-ethyl-3,5-dimethyloctane1

2

3

658

74

4-ethyl

3-methyl and 5-methyl = 3,5-dimethyl

Octane

1. Identify substituents, give each a number (C it is connected to)• Two or more identical substituents: use prefixes (di-,

tri-, tetra-, etc.)2. List substituents alphabetically before root name

• Do not alphabetize prefixes3. Punctuation: commas separate numbers from

each otherhyphens separate numbers from

namesno space between last substituent

& root name



isopropyl

isobutyl

sec-butyl

tert-butyl

alphabetized as “i”

alphabetized as “i”

alphabetized as “b”

alphabetized as “b”

CH CH2 CH3

CH3

C CH3

CH3

CH3

CH CH3CH2

CH3

CH CH3

CH3R

R

R

R

R

R

R

R

Remember that R = any carbon chain

“iso” indicates symmetry

3 carbons

4 carbons

2o

2o

Secondary carbon

Tertiary carbon

3o 3o

HC H

H

H CC C

H H

HHH

CH

HH

2 - methylbutanebutane


Expanded Structure Line Structure

H C

C C C

H

H

CH3

CH3HH

H

C

C

H

H

H

H

H

hexane3,3-dimethyl

1 2 3

4

5

61

2

3

456

hexane4,4-dimethyl

Lowest sum of numbers is correct


Line Structure

Alkanes are written with structural formulas that are expanded to show each bond (Lewis Structure). condensed to show each carbon atom and

hydrogen atoms attached to that carbon.

Expanded (Lewis) Condensed H

H C H CH4 , methane

H


Condensed formulas are written for expanded structural formula by showing each carbon and the attached hydrogen atoms.

Expanded Condensed H H H H │ │ │ │H─C ─C ─C ─C ─ H CH3─CH2─CH2─CH3 │ │ │ │ H H H H


The names of alkanes are determined by the IUPAC (International Union of

Pure and Applied Chemistry) system. end in –ane. with 1-4 carbons in a chain use prefixes as follows.

Name # Carbons Structural FormulaMethane 1 CH4

Ethane 2 CH3CH3

Propane 3 CH3CH2CH3

Butane 4 CH3CH2CH2CH3


Alkanes with 5-10 carbon atoms in a chain use Greek prefixes.Name # Carbons Structural FormulaPentane 5 CH3CH2CH2CH2CH3

Hexane 6 CH3CH2CH2CH2CH2CH3

Heptane 7 CH3CH2CH2CH2CH2CH2CH3

Octane 8 CH3CH2CH2CH2CH2CH2CH2CH3

Nonane 9 CH3 CH2 CH2CH2CH2CH2CH2CH2CH3

Decane 10 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3

Know the 1st eight alkanes (name and structure)


A. Write the condensed formula for: H H H H H

H C C C C C H H H H H HB. What is its molecular formula?

(Gives total # of each atom, does not indicate how they are arranged)

C. What is its name?


CH3─CH2─CH2─CH2─CH3

C5H12

pentane

Hexane is an alkane with six carbon atoms in a

continuous chain. has a “zig-zag” look because each carbon atom

is at the center of a tetrahedron. is represented by a ball-and-stick model as

shown below.


They are cyclic have two hydrogen atoms fewer than the open chain. (remember each carbon has 4 bonds)

are named by using the prefix cyclo- before the name of the alkane chain with the same number of carbon atoms.


The structural formulas of cycloalkanes are usually represented by geometric figures,

Cyclopropane CH2

CH2 CH2

CyclobutaneCH2 CH2

CH2 CH2


Cyclopentane CH2

CH2 CH2

CH2 CH2Cyclohexane

CH2

CH2 CH2

CH2 CH2

CH2



2-methylpropane

or

On piece of your own paper, draw AND name ALL of the isomers for the following alkanes:


Formulas isomers

Pentane

Hexane

Heptane

C5H12

C6H14

C7H16

359


pentane

2-methylbutane

2,2-dimethylpropane


hexane

2-methylpentane

3-methylpentane

2,3-dimethylbutane

2,2-dimethylbutane


heptane

2-methylhexane

3-methylhexane

2,2-dimethylpentane

2,3-dimethylpentane


2,4-dimethylpentane

3,3-dimethylpentane

3-ethylpentane

2,2,3-trimethylbutane

C5H12


(Same formula, different structure)

More branching → weaker London dispersion forces

36.0pentane

27.92-methylbutane

9.52,2-dimethylpropane

Boiling point (°C)NameStructure

BP/MP of Linear alkanes > BP/MP of branched alkanes


Formulas # isomersC4H9IC3H6Cl2C5H11BrC4H8Cl2

4489

II

II


1-iodobutane

2-iodo-2-methylbutane

2-iodobutane

1-iodo-2-methylbutane

I

II

I

Cl

ClCl

Cl

ClClClCl


1,1-dichloropropane

1,3-dichloropropane

1,2-dichloropropane

2,2-dichloropropane

BrBr

Br


Br

1-bromopentane 2-bromopentane

1-bromo-3-methylpentane3-bromopentane

Br


Br

Br

Br

1-bromo-2-methylbutane 2-bromo-3-methylbutane

1-bromo-2,2-dimethylbutane 2-bromo-2-methylbutane

Cl

ClCl

Cl

Cl

ClCl

Cl


1,1-dichlorobutane 1,2-dichlorobutane

1,3-dichlorobutane 1,4-dichlorobutane

Cl Cl

Cl

Cl

ClCl

ClCl


Cl

Cl

2,2-dichlorobutane

1,1-dichlorobutane

2,3-dichlorobutane

1,2-dichloro-2-methylpropane

1,3-dichloro-2-methylpropane

Alkanes are nonpolar. insoluble in water. less dense than water. flammable in air.


Alkanes with 1-4 carbon atoms are

methane, ethane, propane, and butane.

gases at room temperature.

used as heating fuels.


Alkanes with 5-8 carbon atoms are liquids at room temperature. pentane, hexane, heptane, and octane. very volatile. used to make gasoline.

Alkanes with 9-17 carbon atoms are liquids at room temperature have higher boiling points. are found in kerosene, diesel, and jet

fuels.


Combustion exothermic reaction alkanes used as fuel source


C4H10 + ___ O2 ___ CO2 + ___ H2O4 513/2

Incomplete Combustion with insufficient O2 produces CO• Poor ventilation, cigarettes

C4H10 + ___ O2 ___ CO + ___ H2O4 59/2

CO is poisonous because it binds to the hemoglobin in the blood, preventing the absorption of O2

In excess oxygen alkanes burn according to the following equation:

CnH2n+2 +(1.5n+0.5)O2 nCO2 +(n+1)H2O This is called complete combustion,

however if there is insufficient oxygen present incomplete combustion can occur.

CnH2n+2 +(n+0.5)O2 n CO +(n+1)H2O With even less oxygen soot is formed.


In combustion reactions, alkanes react with

oxygen. CO2, H2O and energy

are produced.Alkane + O2 CO2 +

H2O + heat


Mechanism◦How the reaction occurs through

multiple steps (most reactions actually occur in many steps)

Chain Reaction◦Reactions that occur on their own after

some initiating event Free Radicals

◦Atoms that have one free electron—highly reactive


Initiation Step◦ Step where a bond is split by heat/light, producing

free radicals Propagation Step

◦ Step where free radicals react with non-radicals, producing more free radicals and continuing the “chain reaction”

Termination Step◦ Step where free radicals react with each other,

producing non-radicals and terminating the “chain reaction”


Initiation

Propagation

Propagation

Termination

Radical Halogenation of Alkanes


Mechanism (chain reaction):

Step 1 Cl2 ⇌ Cl· + Cl ·

Step 2 Cl· + CH4 CH3· + HCl

Step 3 CH3· + Cl2 CH3Cl + Cl·

Step 4 Cl· + Cl· Cl2Overall reaction: CH4 + Cl2 CH3Cl + HCl

Halogenated product is a haloalkaneNaming: halogen atom is a substituent, replace –ine ending with –o

-F fluoro -Cl chloro -Br bromo -I iodo

chloromethane

h(Free Radicals)

Why not 1-chloromethane?

Type of Step

CH4 + Cl2 CH3Cl + HCl

Halogen substitutes for hydrogen in alkane →multiple results


CH4 CH3Cl CH2Cl2 CHCl3 CCl4

Cl2

Cl2

Cl2

Cl2

CompoundCH3Cl

CH2Cl2CHCl3CCl4

IUPAC NameChloromethaneDichloromethaneTrichloromethaneTetrachloromethane

Common NameMethyl chlorideMethylene chlorideChloroformCarbon tetrachloride

All are liquids at room temperature• Heavy Cl atoms increase LDF• Polar C-Cl bonds – can have polar molecules

Chemistry: An Intro to General,Organic and Biological Chemistryby Timberlake (Green/Tan Book)


1 23

4 56

F Cl

F

Cl

IBr

Cl

Br


5-chloro-2-fluorohexane

2-chloro-5-fluorohexane 2-chloro-4-fluoro-2,3-dimethylpentane

2-bromo-3-ethyl-4-iodopentane 2-bromo-4-chloro-3-isopropylpentane

Two equal numbering options? Number based on alpha order

12

34

5

6

ClCl


?

BrBr

+ Cl2 → OR

1-chloropropane 2-chloropropane

+ Br2 → OR

1-bromo-2-methylbutane 2-bromo-2-methylbutane

Remember that any H on the alkane can be replaced by a halogen

ClOR

3-chloropropane?

+ HCl?

?


BrBr

BrBr

Br

+ Br2 → OR

OROR

1-bromo-2-methylbutane





naming alkanes 2/19/2016dr seemal jelani chem-1601

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