PROBLEM 7.33 - Organic Chemistry

Question

Question: Which solvents favor S_N1 reactions and which favor S_N2 reactions?

_a.

b.  CH₃CN

c.

d.

Step-by-Step Solution

Answer

Answer

a.This solvent favors the S_N1  mechanism.

b.This solvent favors the  S_N2  mechanism.

c.This solvent favors the S_N1  mechanism.

d.This solvent favors the  S_N2  mechanism

S N 1 reactions

This is a two-step reaction. 

In these reactions, the leaving group leaves first, forming a carbocation. The carbocation is then attacked by the nucleophile. 

The rate of the reaction depends upon the leaving group and the nature of the nucleophile. 

The polar protic solvents favors the S_N1  mechanism.

S N 2 Reations

These reactions do not involve the formation of the carbocation.

 In this reaction, one bond is broken, and another bond is formed simultaneously. 

The polar aprotic solutions undergo the S_N2 mechanism.

Comparison of the following compounds

a. CH₃CH₂OH is a polar protic solution. It contains a ^-OH group and hence forms an H-bond. Therefore, this favors the S_N1 mechanism.

 b.CH₃CN is a polar aprotic solution as no hydrogen atom is bonded directly to the highly electronegative atom. Hence, this favors the S_N2   mechanism.

 c. CH₃COOH is a polar protic solution. Hence, it favors the S_N1 mechanism.

 d.CH₃CH₂OCH₂CH₃ is a polar aprotic solution as no hydrogen atom is bonded directly to the highly electronegative atom, i.e., no O-H bonds are present. Hence, this favors the S_N2  mechanism.