Question

3.
Which alkyl halide from the following pairs would you expect to react more rapidly
by an Sn2 mechanism? Explain your answer.
a) CH3CH CH CH Br CH3CH2CHCH
or
Br
CH3
b) CH3CH2CHCH; or
H3-C-Br
Br
CH
c) CH CH CHCHBror
CH3CH2CHCH Br
CH :
CH3

Answer 1

Explanation:

2-Bromobutane is 2° alkylhalide whereas 2-bromo-2-methylpropane is 3° alkyl halide. Therefore, greater numbers of substituents are present in 3° alkyl halide than in 2° alkyl halide to hinder the approaching nucleophile. Hence, 2-bromobutane reacts more rapidly than 2-bromo-2-methylpropane by an SN2 mechanism.