SCH 4U
Cycloalkanes
Text assignment: Parts of:
Page 18 # 3 - 6
Page 21 # 7, 8
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Representative Hydrocarbons
Alkanes
P Principle sources of alkanes are natural gas and
petroleum
P Smaller alkanes (C1 to C4) are gases at room
temperature
Methane is
P A component of the atmosphere of many
planets
P Major component of natural gas
P Produced by primitive organisms called
methanogens found in mud, sewage and cows'
stomachs
The number of constitutional isomers possible for a given
molecular formula increases rapidly with the number of carbons
Nomenclature of Cycloalkanes
P The prefix cyclo is added to the name of
the alkane with the same number of
carbons
P When one substituent is present it is
assumed to be at position one and is not
numbered
Cycloalkanes
Cyclopropane
CH2
CH2
CH 2
Cyclobutane
CH2
CH2
CH 2
CH2
More Cycloalkanes
Cyclopentane
CH2
CH2 CH2
CH2 CH2
Cyclohexane
CH2
CH2 CH2
CH2 CH2
CH2
t Conformations of Cyclohexane
The chair conformation has no ring strain
All bond angles are 109.5 o and all C-H bonds are perfectly staggered
The boat conformation is less stable because of flagpole
interactions and tortional strain along the bottom of the boat
The twist conformation is intermediate in stability between the
boat and the chair conformation
Naming Cycloalkanes with
Side Groups
Number of
side groups
One
Two
Naming
Side group name goes in front
of the cycloalkane name.
Number the ring in the direction
that gives the lowest numbers
to the side groups.
Cycloalkanes with Side
Groups
CH3
methylcyclopentane
CH3
CH3
1,2-dimethylcyclopentane
CH3
CH3
1,2,4-trimethylcyclohexane
CH3
Nomenclature of Cycloalkanes
More than one substituent
P With two alkyl substituents, the one with
alphabetic priority is given position 1
(Or 3-Ethyl-1-methylcyclohexane)
Nomenclature of Cycloalkanes
More than one substituent
P If a long chain is attached to a ring with fewer
carbons, the cycloalkane is considered the
substituent
Multiple cyclic substituents
t Bicyclic compounds
Bicyloalkanes contain 2 fused or bridged rings
The alkane with the same number of total carbons is used as the
parent and the prefix bicyclo - is used
The number of carbons in each bridge is included in the middle o f
the name in square brackets
Physical Properties
Boiling points
Learning Check Alk8
CH 3
CH 3
CH 3
CH3
CH3
Solution Alk8
CH 3
1,2-dimethylcyclobutane
CH 3
CH 3
methylcyclopentane
CH 3
1,3-dimethylcyclohexane
CH3