Question

Which of the following is a nucleophilic addition reaction?
A. $C{H_3}CHO + NaHS{O_3} \to C{H_3}CH(OH)S{O_3}Na$
B. $C{H_3}CHO + N{H_2}OH \to C{H_3}CH = NOH$
C. $3(C{H_3} - CHO) \to {(C{H_3} - CHO)_3}$
D. $C{H_3}CHO + 3{I_2} + 4NaOH \to HCOONa + CH{I_3} + 3{H_2}O + 3NaI$

Answer 1

Nucleophilic chemical reactions can be basically explained as chemical reactions which involve the formation of a sigma bond by the nucleophile of a compound, with another electron deficient species. This type of reaction is elementary because one of its key applications involves the conversion of carbonyl groups into different functional groups.

Complete step by step answer:
Since all the reactions given above involve the carbonyl functional group, let us discuss the mechanism of how exactly nucleophilic addition takes place with respect to carbonyl compounds:
Step 01: The carbon atom in the carbonyl group forms a single bond or a sigma bond with the nucleophile.
Step 02: This results in breaking of the pi bond between carbon and oxygen, which results in the formation of an alkoxide intermediate or the single negative ion of oxygen.
Step 03: Hydrogen is added to this site and this results in the formation of an alcohol derivative of the compound.
Upon observation, we can determine that such a change of a carbonyl group to alcoholic derivative of the compound happens only in the first reaction: $C{H_3}CHO + NaHS{O_3} \to C{H_3}CH(OH)S{O_3}Na$ , where the carbonyl group on $C{H_3}CHO$ gets protonated by hydrogen and forms the alcohol derivative of the two compounds combined.

Hence, Option A is the correct option.

Note:
If the carbonyl group in a compound has a substituent that will increase its positive charge on the carboxylic carbon, then the reactivity of the compound towards nucleophilic addition reaction increases. $N{O_2}$ is the most reactive substituent in nucleophilic addition reaction.