Question

Which of the following compounds will show cis-trans isomerism?
(i) ${\left(C{H}_3\right)}_{2}C=CH-C_2{H}_5$
(ii) $C{H}_2=CB{r}_2$
(iii) $C_6{H}_{5}CH=CH-C{H}_3$
(iv) $C{H}_{3}CH=CClC{H}_3$

Answer 1

Cis trans isomerism:
Cis trans isomerism or geometrical isomerism is also known as configurational isomerism. Cis means "on this side of " and trans means "on the other side of ". In the cis orientation, the groups are on the same side of the carbon-carbon double bond. In trans orientation, the groups are present on opposite sides of the double bond.

Conditions required for cis-trans isomerism:

• Rotation must be restricted in the molecule.
• There must be two non-identical groups on each doubly bonded carbon atom.

Compound which shows cis-trans isomerism:
(iii) and (iv) follow the above conditions but structures (i) and (ii) do not follow the above conditions because they have two identical groups are attached to one of the doubly bonded carbon atoms.

Hence, only (iii) and (iv) compounds will show cis-trans isomerism.

Final answer: (iii) and (iv) compounds will show cis-trans isomerism.