Question

For each of the following sets of chemicals, predict their relative reactivity in the given type of reaction mechanism. List them in order (from least reactive to most reactive) and explain why (the one most significant cause for this trend of reactivity).

a) 1-chlorobutane vs 1-chloro-2-butene in S_N1

b) 2-chlorobutane vs 1-chloro-2-butene in S_N1

c) 1-chlorobutane vs 1-chloro-2-methylpropane in S_N2

Answer 1

Reactivity order of alkyla halides towards SN1 reaction as follows:

Methyl < 1° < allyl ~ benzyl < 2° < 3°

Least reactive. Most reactive

(a) 1-chlrobutane is primary (1°) and 1-chloro-2-butene is allylic alkyl halide. Allaylic halid are more reactive than primary alkyl halides.

Hence, 1-chloro-2-butene is more reactive.

1-chlorobutane < 1-chloro-2-butene

(B) 2-chlorobutane is secondary(2°) alkyl halide. 1-chloro-2-butene is allyl halide. Secondary alkyl halides are more reactive than allylic halides.

Hence, 2-chlorobutane ia more reactive than 1-chloro-2-butene

1-chloro-2-butene < 2-chlorobutane

(C) reactivity order of alkyl halides towards SN2 reaction are as follows:

(Least reactive ) 3° < 2° < 1° < CH3-X ( most reactive)

In 1-chlorobutane steric crowding is less than the steric crowding in 1-chloro-2-methylpropane.

Hence 1-chlorobutane is more reactive than 1-chloro-2-merhylpropane.

1-chloro-2-methylpropane < 1-chlorobutane