PROBLEM 7.54 - Organic Chemistry

Question

Question: Pick the reactant or solvent in each part that gives the faster S_N2 reaction.

1. reaction of with OH^- or CH₃CH₂Br 
2. reaction of CH₃CH₂CH₂Cl NaOH or NaOCOCH₃
3. reaction of  CH₃CH₂CH₂I with ^-OCH₃ in or DMSO

Step-by-Step Solution

Answer

Answer 

1. The reaction of OH^- with CH₃CH₂Br  is faster as compared to the reaction between  OH^- and CH₃CH₂Cl  .
2. The reaction of CH₃CH₂CH₂Cl with NaOH is faster.
3. The reaction of CH₃CH₂CH₂I with ^-OCH₃ by using DMSO as a solvent will be faster. 

Factors affecting the S N 2 reactions

The mechanism of the S_N2  reactions depends upon the following factors:

• The presence of strong nucleophiles favors the S_N2  mechanism.
• The use of a polar aprotic solvent also favors the  S_N2 reactions. 
• A better leaving group also increases the rate of a  S_N2 reaction.
• The presence of a strong nucleophile also favors the S_N2 reaction.

This is because the presence of a strong nucleophile will result in the formation of the transition state quickly. The rate of the reaction also depends upon the concentration of the nucleophile.

The faster S N 2 reactions among the reactions are as follows:

a. The reaction of  OH^- with CH₃CH₂Br  is faster as compared to the reaction between OH^- and CH₃CH₂Cl  .

This Br^- is because the  is a better leaving group as compared to the Cl^-  ion. 

b. The reaction of CH₃CH₂CH₂Cl  with NaOH is faster. The NaOH will produce OH^- which is a stronger nucleophile as compared to OCOCH₃. 

 

c.The reaction of CH₃CH₂CH₂I with ^-OCH₃by using DMSO as a solvent will be faster.

DMSO refers to dimethyl sulfoxide has a chemical formula of (CH₃)₂SO . It is a polar aprotic solvent. The rate of S_N2 the  reaction increases by using the aprotic solvent. 

 On the other hand, methanol (CH₃OH) is a polar protic solvent and is unfavorable for the  reactions.