Question

Which of the following compounds gives a secondary alcohol upon reaction with methylmagnesium bromide?

Options

• Butyl formate

• Pentanal

• 3-pentanone

• Methyl butanoate

Answer 1

Pentanal

Explanation:

(A)

\[\begin{array}{cc}
\phantom{..........}\ce{O}\phantom{....................................................}\ce{O}\phantom{........................}\ce{OH}\phantom{...........}\\
\phantom{.......}||\phantom{....................................................}||\phantom{.........................}|\phantom{..........}\\
\phantom{}\ce{\underset{Butyl formate}{H - C - OCH2} - CH2 - CH2 - CH3 + \underset{1 mol}{CH3MgBr} -> H - C - CH3 ->[CH3MgBr][1 mol] CH3 - C - CH3}\phantom{}\\
\phantom{.............................................................................}|\\
\phantom{.............................................................................}\ce{\underset{2° alcohol}{H}}
\end{array}\]

(B)

\[\begin{array}{cc}
\phantom{.........................}\ce{O}\phantom{..........................................}\ce{OH}\phantom{..}\\
\phantom{.....................}||\phantom{...........................................}|\phantom{}\\
\ce{\underset{Pentanal}{CH3 - CH2 - CH2} - CH2 - C - H + \underset{1 mol}{CH3MgBr} -> CH3CH2CH2CH2 - C - CH3}\\
\phantom{.................................................................}|\\
\phantom{.................................................................}\ce{\underset{(2° alcohol)}{H}}
\end{array}\]

(C)

\[\begin{array}{cc}
\phantom{...}\ce{O}\phantom{........................................}\ce{OH}\phantom{.....}\\
\phantom{}||\phantom{.........................................}|\phantom{....}\\
\ce{CH3CH2 - \underset{3-Pentanone}{C - CH2}CH3 + \underset{1 mol}{CH3MgBr} -> CH3CH2 - C - CH2 - CH3}\\
\phantom{.......................................}|\\
\phantom{..........................................}\ce{\underset{(3° alcohol)}{CH3}}
\end{array}\]

(D)

\[\begin{array}{cc}
\phantom{...........}\ce{O}\phantom{............................................}\ce{OH}\phantom{}\\
\phantom{.........}||\phantom{.............................................}|\phantom{}\\
\ce{CH3CH2\underset{Methyl butanoate}{CH2 - C - OC}H3 + \underset{2 mol}{CH3MgBr} -> CH3CH2 - CH2 - C - CH3}\\
\phantom{.......................................................}|\\
\phantom{..........................................................}\ce{\underset{(3° alcohol)}{CH3}}
\end{array}\]