Question

A haloalkane undergoes S_N2 or S_N1 reaction depending on:

• A. Solvent used in the reaction
• B. Low temperature
• C. The type of halogen atom
• D. Stability of the haloalkane

Answer 1

The Correct Option is A

• S₁ (Unimolecular Nucleophilic Substitution) and S₂ (Bimolecular Nucleophilic Substitution) are two different types of nucleophilic substitution reactions that a haloalkane can undergo.
• S₂: This mechanism occurs when the nucleophile attacks the carbon attached to the halogen in a single concerted step. This is favored by polar aprotic solvents (like acetone or DMSO), which do not solvate the nucleophile strongly and allow it to attack more effectively.
• S₁: This mechanism occurs in two steps, involving the formation of a carbocation intermediate. This is favored by polar protic solvents (like water or alcohols), which stabilize the carbocation intermediate and facilitate the reaction.

Thus, the solvent used in the reaction plays a crucial role in determining whether the reaction will proceed via the S₁ or S₂ mechanism, making option (A) the correct answer.

Answer 2

The type of reaction (S₂ or S₁) that a haloalkane undergoes depends on the solvent used. In polar aprotic solvents, S₂ reactions are favored, whereas in polar protic solvents, S₁ reactions are more likely. The stability of the carbocation and the nature of the leaving group also play a role, but the solvent is the primary factor in determining whether the reaction proceeds via an S₁ or S₂ mechanism.