Cycloalkanes
Cycloalkanes
• Compounds that contain rings of carbon
atoms
• Have the general formula CnH2n
• Represented by polygons in skeletal
drawings
cyclopropane
cyclobutane
cyclopentane
Naming cycloalkanes
1. Count the number of carbon atoms in the
ring and the number in the largest
substituent.
– If the number of carbon atoms in the ring
is equal to or greater than the number in
the largest substituent, the compound is
named as alkyl-substituted cycloalkane.
Substituted cycloalkane
Cycloalkyl-substituted
alkane
Methylcyclopentane
3 carbons
4 carbons
1-cyclopropylbutane
2. For alkyl-substituted cycloalkanes, start
at a point of attachment and number the
substituents on the ring so as to arrive at
the lowest sum.
2
6
1
1
3
5
6
2
4
4
5
3
1,3-dimethylcyclohexane NOT 1,5-dimethylcyclohexane
3. When two or more different alkyl groups
or halogens are present, number them
by alphabetical priority.
CH3
CH2CH3
1-ethyl-2-methylcyclopentane
NOT
2-ethyl-1-methylcyclopentane
Cis-trans isomers
• Because there is not free rotation in
cycloalkanes, geometric isomers called
stereoisomers are formed.
• Cis (L. “on the same side”)
• Trans (L. “across from”)
• Geometric isomers do not convert back
and forth.
H
H
H
H
H
H
H
Cl
Cl
H
H
H
Cl
H
H
H
H
H
H
H
Cl
H
H
H
trans-1,4-dichlorocyclohexane
cis-1,4-dichlorocyclohexane
Chair Conformation
Homework
Page 320: 39-43