Alkanes and Cycloalkanes

Alkanes and CycloalkanesHydrocarbons (contain only carbon and hydrogen)

a) Saturated: (Contain only single bonds)Alkanes (CnH2N + 2 )Cycloalkanes (CnH2N )

b) Unsaturated: contain Alkenes: double bonds (,,,CnH2N) Alkynes: triple bonds ((CnH2N - 2)Aromatic: benzene like compounds

Sources of alkanesPetroleum and natural gas are the two

most important natural sources of alkanes.

Where do we use alkanes in everyday life?Propane in grills/stoves, butane in lighters,

gasoline in autos, and oil in auto engines

The structure of alkanes

Groups attached to the main chain are called substituents. Saturated substituents that contain only carbon and hydrogen are called alkyl groups. An alkyl group is named by taking the name of the alkane with the same number of carbon atoms and changing the - ane ending to -yl

Alkyl groups

CH3 CH3CH3 C

H2 CH3 CH3

CH3

CH3 CH3

CH3CH3

CH2

CH3 CH3

CH3

CH3 CH2

CH3

CH3 CH3

CH3

Alkane Alkyl group

CH4Methane

CH3 -Methyl

CH3CH3Ethane

CH3CH2Ethyl

Propane propyl isopropyl

butane butyl sec-butyl

isobutane isobutyl tert-butyl

Nomenclature of substituted alkanes1) Choose the largest continuous chain2) Start numbering (lowest possible numbering)3) List substituents alphabitically.4) Use di, tri, tetra, penta, hexa, hepta, octa, nona, deca for identical

groups5) If two or more different types of substituents are present, they are

listed alphabetically, except that prefixes such as di - and tri - are not considered when alphabetizing.

Examples

Cl

Br

CH3

CH3

CH

CH3

CH3CH3

3-bromo-2-cholropentane 2,4-dimethylheptane 4-isopropyl-2-methylheptane

12

34

5

1234

567

123

4

567

If there are two equally long continuous chains, choose the one with most branches

CH3

CH3

CH3

CH3

1 23 4

5 67

12

3

4 5 67

3-Ethyl-2-methylheptane not 3-isopropylheptane

Physical properties of alkanes1) Water insoluble2) low boiling point, which increases upon

increasing the number of carbons in the alkane3) branched alkanes have lower boiling points

than the corresponding long chain alkanes

• Conformations of Alkanes:• Conformers: Stereoisomers that are interconvertible

by bond rotation

• Cycloalkanes:

• Conformations of Cyclohexane

CH3H

CH3

H

flip

Chair conformation

Boat conformation

axial

equatorial

flip

5% 95%

flip

0% 100%

methylcyclohexane tert-butylcyclohexane

Reactions of Alkanes:1. Oxidation and Combustion; Alkanes as Fuels Combustion of hydrocarbons is an oxidation in

which C-H bonds are replaced by C-O bonds Exothermic reactions produce heat.

2 .Halogenation of Alkanes

• Draw the monochloro and dichloro products expected from chlorination of propane

CH3 CH2

ClCH3 CH3

Cl

Cl

ClCl

Cl Cl

Cl

Cl

Cl