Question

An organic compound A which is a Grignard reagent is used to obtain 2-methylbutan-2-ol on reaction with a carbonyl compound ‘B’. Identify A’ and ‘B’. Write the equation for the reaction between A and B.

Answer 1

An organic compound A is a Grignard reagent; RMgX B is a ketone RCOR’ 

\[\begin{array}{cc}
\phantom{......}\ce{OH}\\
\phantom{....}|\\
\ce{A + B -> CH3 - C - CH2 - CH3}\\
\phantom{....}|\\
\phantom{.......}\ce{\underset{(2-methylbutan-2-ol)}{CH2}}
\end{array}\]

Ketones lead to the formation of tertiary alcohol, so the compound B is a ketone B-Butan-2-one and A is CH₃MgBr.

\[\begin{array}{cc}
\ce{O}\phantom{...................................}\ce{OMgBr}\phantom{........................}\ce{OH}\phantom{....}\\
\phantom{.}||\phantom{....................................}|\phantom{...............................}|\phantom{.......}\\
\ce{\underset{Butanone}{CH3-C-CH2-CH3} + \underset{bromide}{\underset{magnesium}{\underset{Methyl}{CH3MgBr}}} -> CH3-C-CH2-CH3 ->[H^+/Dil. HCl] CH3-C-CH2-CH3}\\
\phantom{.................................}|\phantom{..............................}|\phantom{..}\\
\phantom{..................................}\ce{CH3}\phantom{...........................}\ce{CH2}
\end{array}\]