JEE Main 2024 — Hydrocarbons Question with Solution

Statement (I) explains a characteristic of $${\mathrm{S}}_{\mathrm{N}}2$$ (Substitution Nucleophilic Bimolecular) reactions. In $${\mathrm{S}}_{\mathrm{N}}2$$ reactions, the attack of the nucleophile and the departure of the leaving group occur simultaneously in a single step. This reaction has a back-side attack mechanism, where the nucleophile attacks the electrophilic carbon from the opposite side of the leaving group. This back-side attack leads to the inversion of configuration at the carbon atom undergoing substitution, a phenomenon often referred to as 'Walden inversion'. Thus, $${\mathrm{S}}_{\mathrm{N}}2$$ reactions are stereospecific, leading to the formation of a product with a specific configuration (either inversion or retention of configuration, but typically inversion in the case of $${\mathrm{S}}_{\mathrm{N}}2$$). Therefore, Statement I is true.

Statement (II) concerns $${\mathrm{S}}_{\mathrm{N}}1$$ (Substitution Nucleophilic Unimolecular) reactions, which proceed in two steps: first, the leaving group departs, forming a carbocation intermediate, and then the nucleophile attacks. The attack of the nucleophile can occur from either side of the planar carbocation, resulting in the formation of both enantiomers of the product. When the reactant is chiral, the product is usually a racemic mixture, consisting of equal amounts of both enantiomers, assuming that there is no steric or electronic preference for the attack on the carbocation. This makes $${\mathrm{S}}_{\mathrm{N}}1$$ reactions non-stereospecific. Therefore, Statement II is true as well.

Based on the explanations provided, the correct answer is Option D: Both Statement I and Statement II are true.