Carbonyl Compounds

The Gattermann-Koch reaction is an electrophilic aromatic substitution used for the synthesis of benzaldehyde from benzene. It involves the generation of an electrophile which reacts with the benzene ring. To identify the correct electrophile, we need to evaluate the options given:

• HCO⁺
• HCl + CO₂ + anhydrous AlCl₃
• CO⁺
• CO + anhydrous AlCl₃

In the Gattermann-Koch reaction, the electrophile is formed when carbon monoxide (CO) reacts with hydrochloric acid (HCl) in the presence of a Lewis acid catalyst, usually anhydrous aluminum chloride (AlCl₃). This reaction generates the formyl cation (HCO⁺), which then acts as the electrophile in the reaction with benzene to form benzaldehyde.

Therefore, the correct electrophile involved in the Gattermann-Koch reaction is: HCO⁺.

The reactivity of carbonyl compounds towards nucleophilic addition is influenced by two main factors: the electron-withdrawing effect and steric hindrance. Elecron-withdrawing groups increase reactivity by making the carbonyl carbon more electrophilic, while steric hindrance can decrease reactivity. Let's analyze the provided compounds:

Based on these factors, the increasing order of reactivity towards nucleophilic addition reactions is as follows:

Acetophenone < p-Tolualdehyde < Benzaldehyde < p-Nitrobenzaldehyde.