Question

In a SN2 substitution reaction of the type
R - Br + Cl⁻ □(→┴DMF ) R - Cl + Br⁻
which one of the following has the highest relative rate ?
(a) CH₃ – CH₂ – CH₂Br (b) CH₃ - CH - CH₂Br
|
CH₃
CH₃
|
(c) CH₃ - C - CH₂Br
|
CH₃
(d) CH₃CH₂Br

Answer 1

Following which has the highest relative rate is :

Reaction : R - Br + Cl⁻ □(→┴DMF ) R - Cl + Br⁻

• Already given that above reaction is SN2 type.

(a) CH₃ – CH₂ – CH₂Br ( bromopropane )

(b) CH₃ - CH - CH₂Br ( 1-bromo-2-methyl propane )

|

CH₃

CH₃

|

(c)CH₃ - C - CH₂Br (1-bromo-2,2-dimethyl propane)

|

CH₃

(d) CH₃CH₂Br ( 1-bromo ethane )

• Increasing order of steric hindrance in the given compound is as below :

(c) > (b) > (a) > (d)

• Therefore, Increasing order of SN2 reaction is :

(c) < (b) < (a) < (d)

• (d) i.e 1-bromo ethane, has the highest relative rate