Question

The order of reactivity of Phenyl Magnesium Bromide with the following compounds is:

• A. $\left(II\right)>\left(III\right)>\left(I\right)$
• B. $\left(I\right)>\left(III\right)>\left(II\right)$
• C. $\left(II\right)>\left(I\right)>\left(III\right)$
• D. All react with the same rate

Answer 1

The correct option is C $\left(II\right)>\left(I\right)>\left(III\right)$

Nucleophile attacks the most electrophilic site first. Among aldehyde and a ketone, aldehydes are more electrophilic as in ketones the + charge on carbonyl carbon is decreased by $+I$ effect of both alkyl groups.

Moreover in the tetrahedral intermediate aldehydes have less steric repulsion than ketone and aldehyde increases the -ve charge on oxygen less in comparison to ketones.

Based on the above the order of reactivity is (II) > (I) > (III)