Question

A nucleophilic substitution reaction proceeds through $S _{ N } 1$ mechanism. So, the reaction is

• A. unimolecular
• B. bimolecular
• C. trimolecular
• D. rate depends on concentration of incoming nucleophile

Answer 1

The Correct Option is A

A nucleophilic substitution reaction proceeds through $S_N1 $ mechanism, so the reaction is unimolecular.

Answer 2

Ans: A nucleophilic substitution will proceed through the SN1, it proceeds through a unimolecular reaction. This means that the rate-determining step of the reaction involves only one molecule (unimolecular). The SN1 is a two step process: 

1. Formation  of carbocation: this step is the departure of leaving the group and forming a carbocation intermediate which is a positive charge. 
2. Nucleophilic attack: in the second step, the nucleophile attacks the carbocation and replaces the leaving group, this results in the substitution product. 

The characteristics of nucleophilic substitution are as follows: 

• Racemization: Because of the carbocation intermediate, the attack of the nucleophile can be from either side. Therefore there is a formation of a racemic mixture. 
• Solvent effect: Solvents like water and alcohols make the carbocation and the transition state stable. 
• Tertiary carbocation: SN1 reaction is more preferred on the compounds that form a stable tertiary carbocation as they are more stable than primary and secondary carbocation.