JEE Advanced 2013 · Paper 1 · Chemistry Q30 · Dronacharya Exams

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ChemistrySingle correct+2Question 30 of 60

KI in acetone, undergoes $\mathrm S_\mathrm N2$ reaction with each of P, Q, R and S. The rates of the reaction vary as

Four chlorides: P chloromethane CH₃Cl; Q 2-chloropropane; R allyl chloride (3-chloroprop-1-ene); S phenacyl chloride (2-chloro-1-phenylethan-1-one, PhCOCH₂Cl).

A

P > Q > R > S

B

S > P > R > Q

C

P > R > Q > S

D

R > P > S > Q

Answer and worked solution

Official answer: B

SN2 reactivity.

S (phenacyl chloride): the adjacent C=O greatly stabilises the SN2 transition state, fastest.
P (CH₃Cl): unhindered methyl.
R (allyl chloride): primary and allylic, fast but behind methyl here.
Q (2-chloropropane): secondary, hindered, slowest.

Order S > P > R > Q.

(B)

Topics:SN1 and SN2

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