Question

Which cycloalkanes show cis, trans isomerism? For each that does, draw both isomers.

Short answer

Answer: Cyclobutane, cyclopentane, and cyclohexane can all exhibit cis-trans isomerism. The structures of the two isomers for each are as follows: Cyclobutane: 1. Cis-1,2-dimethylcyclobutane 2. Trans-1,2-dimethylcyclobutane Cyclopentane: 1. Cis-1,2-dimethylcyclopentane 2. Trans-1,2-dimethylcyclopentane Cyclohexane: 1. Cis-1,2-dimethylcyclohexane 2. Trans-1,2-dimethylcyclohexane

Step-by-step solution

Identify the minimum number of carbons for a cycloalkane to exhibit cis-trans isomerism

A cycloalkane must have at least 4 carbon atoms to be able to form cis-trans isomers. This is because it requires at least two substituted carbons to have different groups attached to them, with the remaining carbons forming the ring structure. Cyclopropane does not have enough carbons to support cis-trans isomerism.

Cyclobutane

Cyclobutane is a cycloalkane with 4 carbon atoms. To show cis-trans isomerism, there must be two substituted carbons with different groups attached. The isomers can be drawn as follows: Cis-1,2-dimethylcyclobutane: ``` H H \ / H--C=C--H | | C-H | H ``` Trans-1,2-dimethylcyclobutane: ``` H H \ / H--C=C--H | | C-H \ H ``` Thus, cyclobutane can show cis-trans isomerism.

Cyclopentane

Cyclopentane is a cycloalkane with 5 carbon atoms. To show cis-trans isomerism, there must be two substituted carbons with different groups attached. The isomers can be drawn as follows: Cis-1,2-dimethylcyclopentane: ``` H H \ / H--C=C--H | | H--C H | H ``` Trans-1,2-dimethylcyclopentane: ``` H \ C | H H-C \ / | C=C--H |\ H H ``` Thus, cyclopentane can also show cis-trans isomerism.

Cyclohexane

Cyclohexane is a cycloalkane with 6 carbon atoms. To show cis-trans isomerism, there must be two substituted carbons with different groups attached. The isomers can be drawn as follows: Cis-1,2-dimethylcyclohexane: ``` H | H-C-- | \ H-C=C--H | | H--C H | H ``` Trans-1,2-dimethylcyclohexane: ``` H | H--C H / C--C / / H C--H |/ \ H H ``` Thus, cyclohexane can also show cis-trans isomerism.