Question

Arrange the following compounds in increasing order of reactivity towards nucleophilic addition reaction. (I)$C_6H_5COCH_3$ (II) $CH_3 CO-C_2H_5$ (III)$C_6H_5CHO$ (IV) $Cl-CH_2 - CHO$

• A. IV > III > II > I
• B. IV > II > III > I
• C. I > II > III > IV
• D. III > IV > II > I

Answer 1

Answer: (A)

IV > III > II > I

Answer 2

electron releasing alkyl groups in ketones make the carbon less electron deficient in comparison to aldehydes. Therefore ketones are less reactive than aldehydes towards nucleophilic addition reactions. Aromatic aldehydes and ketones are less reactive than corresponding aliphatic aldehydes and ketones due to $+R$ effect of benzene ring. Aromatic aldehydes are more reactive than alkyl aryl ketones which in turn are more reactive than diaryl ketones. Since $-C l$ is more electronegative than carbon, it increases the reactivity. So, the order is $\underset{(IV)}{Cl-CH_{2}- CHO} > \underset{(III)}{C_{6}H_{5}CHO} > \underset{(II)}{CH_{3}COC_{2}H_{5}} > \underset{I}{C_{6}H_{5}COCH_{3}}$