Chemistry MCQs for NEET — Practice Questions with Answers

(d) The chain termination step involves the combination of two radicals.

(b) The chain propagation step involves the use of free radical and regeneration of another free radical.

(d) These are characteristics of carbanion

(d) These are characteristics of S_N1 mechanism.

(d) Elimination reactions involves removal of a molecule (HBr here) from a substrate.

(a) The S_N2 mechanism always involves 100% inversion since nucleophile attack from back side of leaving group.

$$\begin{gathered} \mathrm{R}-\mathrm{X}\stackrel{{\mathrm{OH}}^{-}}{\to }\mathrm{O}\stackrel{-}{\mathrm{H}}---\mathrm{R}---\mathrm{X} \\ \downarrow \\ \mathrm{OH}-\mathrm{R}+{\mathrm{X}}^{-}: \end{gathered}$$

$\left(\mathrm{b}\right) {\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH} \underset{∆}{\overset{{\mathrm{H}}_2{\mathrm{SO}}_4}{\to }}{\mathrm{CH}}_2={\mathrm{CH}}_2 +{\mathrm{H}}_2\mathrm{OC}$

The formation of cyanohydrin from a ketone is an example of a nucleophilic addition reaction. In this reaction, the cyanide ion (CN⁻) acts as a nucleophile and attacks the electrophilic carbonyl carbon of the ketone, forming a cyanohydrin product.

(c) Steric hindrance in tertiary halides give rise to less reactivity for S_N2.

(b) In S_N1 reaction, there is slight more inversion product than retention product because S_N1 reaction also depends on shielding effect of the front side of the reacting carbon.