Chemistry - Carbonyl compounds Question with Solution | TestHub

In phenyl magnesium bromide, phenyl is attached with that C-atom of carbonyl group which has low electron density (higher electropositive charge). In carbonyl compounds, aldehydes are more reactive, towards nucleophile in nucleophilic addition reactions because in ketones alkyl groups is present on both sides (due to + I effect) which decreases the electropositive charge of carbon of carbonyl group.

Hence, attraction of nucleophile decreases. Moreover in the tetrahedral intermediate, aldehydes have less steric repulsion than ketones and also the aldehyde increases the negative charge on oxygen less in comparison of ketones.

Therefore, the order of reactivity of acetone (I), acetaldehyde (II) and benzophenone (III) with PhMgBr is (II) $>$ (I) $>$ (III).