Question

The best yield of given product can be obtained by using which set of reactants $X$ and $Y$?

• A. $PhLi$ + Neopentyl chloride
• B. $PhMgBr$ + Neopentyl bromide
• C. $t-Bu-MgBr$ + Benzyl bromide
• D. Benzylchloride + t - Butyl chloride $\stackrel{Na}{\to }$

Answer 1

The correct option is C $t-Bu-MgBr$ + Benzyl bromide

$t-butylMgBr$ gives butane as the major product and tertiary Grignard reagent is preferred. The product formed is butane. When Grignard reagent like alkyl$MgBr$ reacts with alkene we get alkane corresponding to the alkyl part of Grignard reagent. In this reagent, the $C$ atom is more electronegative than $Mg$ hence the alkyl part acts as a nucleophile and takes an active $H$ to form the corresponding alkane and here butane.