Question

The $K_{eq.}$ values in HCN addition to following aldehydes are in the order.

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

Answer 1

The correct option is D II $>$ I $>$ III

$Keq=\frac{\left[Product\right]}{\left[reactant\right]}$

1) Refer image 1. It has less positive resonance effect than $NM{e}_2$ hence has more Keq than III as Carbonyl inthis compound is more electrophilic than (III) compound.

2) Refer image 2. Carbonyl groups more electrophilic than (I) and (III) Hence, readily reacts with $HCN and has great Keq than (I) and (III)

3) Refer image 3. $NM{e}_2$ has greater $+R$ effect than $-OMe$, hence react to lesser extent than (I) and II Hence, has least Keq.

$\therefore KeqII>I>III$