QJEEAdv17Che281: JEE Advanced 2017 Chemistry - Class 11 JEEAdv17Che281 Solution: For the following compounds, the correct statement(s) with…

(a) I is a benzylic halide, thus, it undergoes S_N1 reaction easily as benzylic carbocation is resonance stabilized. III also follows S_N1 mechanism as it is 3$${}^{\circ }$$ alkyl halide.

(b) Compounds I and II are 1$${}^{\circ }$$ alkyl halides, then they undergo S_N2 mechanism.

(c) Correct. In S_N1 reaction, the nucleophile approaches the substrate carbon from the back side with respect to the leaving group. Nucleophilic displacement of the leaving group in an S_N2 reaction causes inversion of configuration at the substrate carbon.

(d) Stability of carbocations follows the order:

$$\underset{(IV)}{2^{\circ }benzylic}>\underset{(III)}{3^{\circ }alkyl}>\underset{(I)}{1^{\circ }benzylic}$$