Question

Give the decreasing order of nucleophilic addition reaction of the following :
(i) $HCHO$ (ii) $PhCHO$
(iii) Chloral $({Cl}_{3}C-CH=O)$ (iv) $Acetophenone$

• A. $\left(iii\right)>\left(i\right)>\left(ii\right)>\left(iv\right)$
• B. $\left(iv\right)>\left(ii\right)>\left(i\right)>\left(iii\right)$
• C. $\left(i\right)>\left(iii\right)>\left(ii\right)>\left(iv\right)$
• D. $\left(iii\right)>\left(i\right)>\left(iv\right)>\left(ii\right)$

Answer 1

The correct option is A $\left(iii\right)>\left(i\right)>\left(ii\right)>\left(iv\right)$

Aldehydes are more reactive towards Nucleophillic substitution compared to ketones because of less steric hindrance. In Aldehydes electron withdrawing group increase its reactivity when present.

Here, $CC{l}_3-$ is an electron withdrawing group. So, it increases reactivity.

$CC{l}_3-CHO-$ Electron withdrawing agent.

$HCHO-$ Very less steric hindrance.

$ph-CHO$ Aldehyde- Little bulky.

Acetophenone- Ketone.

$CC{l}_3-CHO>HCHO>ph-CHO>$ Acetophenone