Question 11.7: Which of the following cycloalkanes show cis-trans isomerism...
Which of the following cycloalkanes show cis-trans isomerism? For each that does, draw both isomers.
(a) Methylcyclopentane (b) 1,1-Dimethylcyclobutane
(c) 1,3-Dimethylcyclobutane
Strategy
For a cycloalkane to show cis-trans isomerism, it must have at least two substituents, each on a different carbon of the ring.
(a) Methylcyclopentane does not show cis-trans isomerism; it has only one substituent on the ring.
(b) 1,1-Dimethylcyclobutane does not show cis-trans isomerism because only one arrangement is possible for the two methyl groups. Because both methyl groups are bonded to the same carbon, they must be trans to each other—one above the ring, the other below it.
(c) 1,3-Dimethylcyclobutane shows cis-trans isomerism. The two methyl groups may be cis, or they may be trans.
