In the following compounds, what is the increasing order of their reactivity towards nucleophilic addition reactions?

Benzaldehyde, p-Tolualdehyde, p-Nitrobenzaldehyde, Acetophenone

Acetophenone < p-Tolualdehyde < Benzaldehyde < p-Nitrobenzaldehyde

The correct answer is option 3. Acetophenone < p-Tolualdehyde < Benzaldehyde < p-Nitrobenzaldehyde.

To determine the increasing order of reactivity towards nucleophilic addition reactions for the given compounds (Benzaldehyde, p-Tolualdehyde, p-Nitrobenzaldehyde, Acetophenone), we need to consider the electronic effects of substituents on the carbonyl group and the nature of the carbonyl compound.

Analysis of Each Compound:

Benzaldehyde (\(C_6H_5CHO\)):

Electronic Effects: The phenyl group slightly stabilizes the carbonyl group through resonance but has a relatively neutral effect overall.

Reactivity: It has moderate reactivity towards nucleophilic addition.

p-Tolualdehyde (\(p-CH_3C_6H_4CHO\)):

Substituent Effect: The methyl group (\(CH_3\)) at the para position is an electron-donating group via the inductive effect and hyperconjugation.

Reactivity: The electron-donating effect of the methyl group reduces the electrophilicity of the carbonyl carbon, making it less reactive towards nucleophiles compared to benzaldehyde.

p-Nitrobenzaldehyde (\(p-NO_2C_6H_4CHO\)):

Substituent Effect: The nitro group (\(NO_2\)) at the para position is a strong electron-withdrawing group through both inductive and resonance effects.

Reactivity: The electron-withdrawing effect of the nitro group increases the electrophilicity of the carbonyl carbon, making it more reactive towards nucleophiles compared to benzaldehyde.

Acetophenone (\(C_6H_5COCH_3\)):

Nature of Carbonyl Group: As a ketone, the carbonyl carbon in acetophenone is less electrophilic compared to aldehydes because of the electron-donating effect of the alkyl group (\(CH_3\)).

Reactivity: Ketones are generally less reactive towards nucleophilic addition than aldehydes due to steric and electronic factors.

Increasing Order of Reactivity: Combining these considerations, the order of reactivity towards nucleophilic addition reactions is:

Acetophenone: Least reactive because it is a ketone and the carbonyl carbon is less electrophilic.

p-Tolualdehyde: Less reactive than benzaldehyde due to the electron-donating effect of the methyl group.

Benzaldehyde: More reactive than p-tolualdehyde and acetophenone.

p-Nitrobenzaldehyde: Most reactive due to the strong electron-withdrawing effect of the nitro group.

Therefore, the increasing order of their reactivity towards nucleophilic addition reactions is: 3. Acetophenone < p-Tolualdehyde < Benzaldehyde < p-Nitrobenzaldehyde