Question

Find out the correct order of reactivity of the given compounds with respect to $S_{N}2$.

• A. p > s > q > r
• B. r > q > s > p
• C. s > p > r > q
• D. q > r > p > s

Answer 1

The correct option is A p > s > q > r

p) In the substrate p, the carbonyl group increases the electrophilicity of the carbon next to it towards nucleophilic substitution reaction. since it is also a primary alkyl halide it is the most reactive towards $S_{N}2$ reaction.

s) It also has electron withdrawing group next to the reactive site. Hence it is the second most reactive.

q) Allylic halides are more reactive than secondary halides to $S_{N}2$ reactions due to the stabilisation of the transition state in the case of allylic halides via resonance.

r) It is a secondary halide and which is also crowded and hence it is the least reactive towards $S_{N}2$.

Hence the reactivity order is: p > s > q > r