Given below are two statements :
Statement (I) : S_N 2 reactions are 'stereospecific', indicating that they result in the formation of only one stereo-isomer as the product.
Statement (II) : S_N 1 reactions generally result in formation of product as racemic mixtures.
In the light of the above statements, choose the correct answer from the options given below :

Solution

Chemistry ma’am · 4 steps

Ask how the nucleophile arrives: SN2 from the back only, SN1 at a flat carbocation from either face.

1. SN2 is one step. The nucleophile attacks the carbon from the side opposite the leaving group, in a single step. This backside attack always inverts the configuration (Walden inversion), so one stereoisomer of the substrate gives only one stereoisomer of the product. That is what stereospecific means, so Statement I is true.
2. SN1 goes via carbocation. The leaving group departs first and leaves a carbocation. It is sp² hybridised and planar, so the nucleophile can attack from either face with nearly equal chance.
3. Both faces open. Attack from one face keeps the configuration and attack from the other face inverts it. An optically active substrate therefore gives a racemic mixture, usually with a slight excess of the inverted product. Statement II is true.
4. So. Both statements are true, which is option (d).

The idea to keep. Ask whether the carbon ever goes flat. SN2 never does, so it gives inversion and one product. SN1 passes through a planar carbocation, so it gives racemisation.

Answer from the NTA final answer key. Solution by PrepWiser.