MCQ Detailed View

Aldehydes are organic compounds characterized by the presence of a carbonyl group (C=O) bonded to at least one hydrogen atom. The carbonyl carbon in aldehydes is highly electrophilic due to the partial positive charge it acquires, making it susceptible to attack by nucleophiles. As a result, the most common and characteristic reaction of aldehydes is nucleophilic addition.

In nucleophilic addition reactions, a nucleophile donates an electron pair to the carbonyl carbon. This leads to the breaking of the π-bond in the carbonyl group and formation of a tetrahedral intermediate. Depending on the reactants and conditions, this intermediate can then be protonated or further modified to give various products.

A classic example is the addition of hydrogen cyanide (HCN) to an aldehyde, forming a cyanohydrin. Similarly, aldehydes react with alcohols in the presence of acid to form hemiacetals and acetals. Addition of Grignard reagents to aldehydes results in the formation of secondary alcohols. These reactions underline the importance of the nucleophilic addition mechanism in aldehyde chemistry.

The other options are not typical for aldehydes. Electrophilic addition reactions are more characteristic of alkenes. Nucleophilic substitution usually occurs in compounds with good leaving groups, such as alkyl halides. Nucleophilic elimination is less common in carbonyl chemistry and involves different mechanisms.

Understanding the nucleophilic addition reaction is crucial for mastering topics such as aldehyde reactivity, synthesis of alcohols, and functional group transformations in organic synthesis. It also forms the basis for many reactions studied in both academic and applied organic chemistry.