Question

Which of the following compounds does not form an alcohol when it reacts with excess Grignard reagent?

A.

B.

C.

Short answer

(a)

(C)

Step-by-step solution

Step-by-Step SolutionStep 1: Reaction of N-methylpropionamide (a)

Generally, aldehydes and ketones give alcohol when reacted with Grignard reagent.

When N-methyl propionamide reacts with excess Grignard reagent, a productive reaction does not take place. Since it has$\mathrm{N}-\mathrm{H}$ bond, this hydrogen reacts with Grignard reagent which then gets converted toalkane.

Step 2: Reaction of methyl propionate (b)

This compound can undergo nucelophilic addition-elimination reaction which forms a ketone. When excess Grignard reagent is added, it undergoes nucelophilic addition reaction and forms a tertiary alcohol. Methyl propionate produces tertiary alcohol when it reacts with Grignard reagent. The reaction is given below.

${\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{COOCH}}_3+\mathrm{RMgX}\to {\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{C}\left({\mathrm{R}}_2\right)\mathrm{OH}$

Reaction of methyl 3-hydroxypropanoate (c)

Methyl 3-hydroxypropanoate has a hydrogen atom bonded with an oxygen atom and cannot undergo nucleophilic addition reaction. Thus, the acidic proton reacts with Grignard reagent and producesalkane.