Alkanes and Cycloalkanes
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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
H2CH3 CH3
CH3
CH3 CH3
CH3CH3
CH2
CH3 CH3
CH3
CH3 CH2
CH3
CH3 CH3
CH3
Alkane Alkyl group
CH4
Methane
CH3 -Methyl
CH3CH3
Ethane
CH3CH2
Ethyl
Propane propyl isopropyl
butane butyl sec-butyl
isobutane isobutyl tert-butyl
Nomenclature of substituted alkanes1) Choose the largest continuous chain
2) Start numbering (lowest possible numbering)
3) List substituents alphabitically.
4) Use di, tri, tetra, penta, hexa, hepta, octa, nona, deca for identical groups
5) 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
12
34
567
12
34
567
If there are two equally long continuous chains, choose the one with most branches
CH3
CH3
CH3
CH3
12
3 45 6
7
12
3
4 5 67
3-Ethyl-2-methylheptane not 3-isopropylheptane
Physical properties of alkanes
1) Water insoluble
2) low boiling point, which increases upon increasing the number of carbons in the alkane
3) 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%
methylcyclohexanetert-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.
If less oxygen is available
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
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