The order of reactivity of pheny1 magnesium bromide with the following compounds is

Options

A. `II gt III gt I`
B. `I gt III gt II`
C. `II gt I gt III`
D. All react with the same rate

Answer

C

Explanation

From phenyl magnessium 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 nucleophillic addition reactions because in ketones alkyl groups (due to +/ effect) decrease the electropositive charge of carbon of carbonyl group. Hence, attraction of nucleophile decreases. Moreover in the tetrahedral intermediate, aldehydes have less stearic rcplusion than ketones and also the aldehyde increases the negative charge on oxygen less in comparison of ketones. Therefore, on the basis of above reason, the order of reactivity of acetone (I), acetaldehyde (II) and benzophenone (III) with `PhMgBr` is `II gt I gt III`