Question

What are \[E\] and \[Z\;\] isomers of cinnamic acid?
A)

and

B)

and

C)

and

D) None of the above

Answer 1

Hint: We have to remember that the cinnamic acid is \[3 - phenylpropanoic acid\]
We can draw the structure of cinnamic acid:

Complete step by step answer:
Before solving this question we will look at the structure of cinnamic acid and more about isomers.
Isomers are molecules with the same molecular formula and different arrangement.
Isomers can be of two types i) structural isomers ii) Stereoisomers
\[E/Z\] isomers come under the category of Stereoisomers.
\[E\] isomer: This notation is used when the groups with higher priority are on the opposite side.
\[Z\]isomer: This notation is used when the groups with higher priority are on the same side.
In case of Cinnamic acid,
It is \[3 - phenylpropanoic acid\]
Structure of \[3 - phenylpropanoic acid\] is

    \[Z - Cinnamic{\text{ }}acid\] $ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \$ \[E - Cinnamic{\text{ }}acid\]
\[E/Z\] isomers are as follows:
Phenyl ring and Carboxylic acid group are the one with higher priority than H atoms.
Out of \[COOH\] and Phenyl ring, \[COOH\] will have the priority as 1 followed by Phenyl ring \[{C_6}{H_5}\], Therefore when both these groups are on the same side, this will represent \[Z - Cinnamic Acid\] i.e. \[Z\;\] isomer.
And when both these groups are on the opposite side, this will represent \[E - Cinnamic Acid\] i.e. \[E\] isomer.
Option A) this is an incorrect option since cinnamic acid is \[3 - phenylpropanoic acid\]but the structure given in this option is not \[3 - phenylpropanoic acid\]thus we can neglect this option.
Option B) This is a correct option as \[3 - phenylpropanoic acid\] is the molecular formula for cinnamic acid.
Option C) this is an incorrect option.
Option D) this is an incorrect option as we got a correct option i.e. B

Hence, the correct option is ‘Option D’

Note: For solving this type of questions one must look at the structural as well as molecular formula for the compound given, this makes it easy to solve the question.