PROBLEM 7.29 - Organic Chemistry

Question

Question: What is the likely mechanism of nucleophilic substitution for each alkyl halide?

a.

b.

c.

   

d.

Step-by-Step Solution

Answer

Answer

a. The likely mechanisms for this alkyl halide are S_N1  and  S_N2 reactions. 

b. The likely mechanism for this alkyl halide is S_N2   reaction.

c. The likely mechanisms for this alkyl halide are S_N1  andS_N2    reactions.

d. The likely mecha1nism for this alkyl halide is S_N1   reaction.

Nucleophilic substitution reaction

Reactions where one nucleophile is substituted in place of another nucleophile are nucleophilic substitution reactions.  

These reactions are identical to displacement reactions

Alkyl halide

Compounds consisting of one or several halogens are alkyl halides. Halogens substitute the hydrogen atoms in alkyl halides

 

Mechanism of nucleophilic substitution for alkyl halide in question a

a. The alkyl halide structure shows that the carbon atom on the bromine is linked to two other carbon atoms. So, the bromine atom is linked to the secondary carbon atom. A secondary carbocation is formed on the removal of bromine. The secondary carbocation gets subjected to nucleophilic substitution via both S_N1  and S_N2 reactions. 

Hence, the likely mechanisms for the alkyl halide are both S_N1  and S_N2    reactions.

Mechanism of nucleophilic substitution for alkyl halide in question b

b. The carbon atom on the bromine is linked to another carbon atom. So, the bromine atom is linked to primary carbon, and the alkyl halide is the primary alkyl halide. The nucleophilic substitution in primary alkyl halide occurs via the S_N2 reaction.

Hence, the likely mechanism for this alkyl halide is  S_N2 reaction.

Mechanism of nucleophilic substitution for alkyl halide in question c

c. The carbon atom situated on the bromine atom is connected to two other carbon atoms. So, the bromine atom is joined to the secondary carbon atom. The bromine removal leads to the generation of secondary carbocation. The nucleophilic substitution for secondary carbocation takes place by S_N1  and S_N2  reactions.

Hence, the given alkyl halide undergoes nucleophilic substitution via both  S_N1  and S_N2   reactions.

Mechanism of nucleophilic substitution for alkyl halide in question d

d. The carbon atom present in bromine is linked to three other carbon atoms in this structure. So, the carbon atom is linked to the tertiary carbon atom. The tertiary carbocation is formed on the removal of bromine. The nucleophilic substitution occurs via S_N1 mechanism for tertiary carbocation. 

Hence, the likely mechanism for this alkyl halide is S_N1  reaction.