Question

Arrange the following in increasing order of their reactivity for nucleophilic addition reaction.

• A. \(a\lt b\lt c\lt d\)
• B. \(a\lt d\lt c\lt b\)
• C. \(c\lt b\lt a\lt d\)
• D. \(c\lt a\lt b\lt d\)

Hint:

Electron-withdrawing groups increase the reactivity of carbonyl compounds toward nucleophilic addition, while electron-donating groups decrease it.

Answer 1

The Correct Option is A

Step 1: Recall the factor affecting nucleophilic addition.
Nucleophilic addition depends on the electrophilicity of the carbonyl carbon.
Greater positive character on carbonyl carbon means greater reactivity toward nucleophilic addition.

Step 2: Compare aldehydes and ketones.
Aldehydes are generally more reactive than ketones because ketones have two carbon groups that create steric hindrance and donate electron density.
Hence, benzophenone \((a)\) is the least reactive.

Step 3: Compare substituted benzaldehydes.
In \(p\)-methylbenzaldehyde \((b)\), the \(-CH_3\) group is electron donating.
It decreases the positive character on the carbonyl carbon, so it is less reactive than benzaldehyde.

Step 4: Effect of nitro group.
In \(p\)-nitrobenzaldehyde \((d)\), the \(-NO_2\) group is strongly electron withdrawing.
It increases the positive character on carbonyl carbon, so it is the most reactive.

Step 5: Final order.
Thus, the increasing order of reactivity is
\[ a\lt b\lt c\lt d \]

Step 6: Final conclusion.
Hence,
\[ \boxed{a\lt b\lt c\lt d} \]