Question

An aromatic compound ${}^{\prime }{A}^{\prime }$ having molecular formula $C_7{H}_6{O}_2$ on treating with aqueous ammonia and heating forms compound ${}^{\prime }{B}^{\prime }$. The compound ${}^{\prime }{B}^{\prime }$ on reaction with molecular bromine and potassium hydroxide provides compound ${}^{\prime }{C}^{\prime }$ having molecular formula $C_6{H}_{7}N$. The structure of ${}^{\prime }{A}^{\prime }$ is :

• A.
• B.
• C.
• D.

Answer 1

Answer: (C)

First, we find the DU of each compound.
$DU\left(C_7{H}_6{O}_2\right)=5$
$DU\left(C_6{H}_{7}N\right)=4$
When $C_7{H}_6{O}_2$ reacts with aqueous ammonia and heated it forms $C_7{H}_{7}ON$.Now, $DU\left(C_7{H}_{7}ON\right)=5$
The reagent $B{r}_2/NaOH$ is classic Hoffman Bromamide reagent and this gives a clue that B may be an Amide. This consumes one DU and by seeing remaining 6 carbon and 5 Hydrogens we can say B is Benzamide.
So Benzamide on Hoffman Degradation gives Aniline which matches with the formula of $C$.
We have to know usually $N{H}_3+$ heat gives an Amide when a carboxylic acid is used as a reagent.
So among the options, we can see option C which is a Benzoic acid matches the formula of $X$ and hence is the correct answer.