Question

There are four compounds with the

formulaC4H9Br. List them in order
ofdecreasing activity in an SN2 reaction.

Answer 1

The four compounds with formula C4H9Br are

1. 1- Bromobutane

2. 2-Bromobutane

3. 1-bromo-2-methyl propane

4. 2-Bromo-2-methyl propane

Reactivity towards SN2 in decreasing order is :

1- Bromobutane > 1-bromo-2-methyl propane > 2-Bromobutane >

2-Bromo-2-methyl propane

Step-by-step explanation:

SN2 reaction : This is also known as second order nucleophilic Substitution Reaction because :

• The rate determining step depends both on the concentration of the substrate as well as nucleophile.

• This reaction involve formation of 5- bond transition state (not the intermediate)

• The bond making and breaking occur simultaneously

• The reactivitey order for SN2 is more for less hindered substrate i.e :

Primary > Secondary > tertiary

Among the isomers of C4H9Br

• The primary halides are : 1- Bromobutane and 1-bromo-2-methyl propane

(Br is attached to primary carbon)

but 1- Bromobutane is less hindered than 1-bromo-2-methyl propane

So,1- Bromobutane > 1-bromo-2-methyl propane

• Secondary :2-Bromobutane

• Tertiary : 2-Bromo-2-methyl propane

Hence order is :

1- Bromobutane > 1-bromo-2-methyl propane > 2-Bromobutane >

2-Bromo-2-methyl propane