91Ó°ÊÓ

The nucleophilic substitution reaction is completed by the attack of the nucleophile on the substrate.

The following points are shown:

• If the attack of nucleophile directly occurs on the substrate, it is bimolecular substitution.
• If the attack of nucleophile occurs on the substrate’s intermediate, it is a unimolecular substitution.
• In the bimolecular substitution, the stereochemistry of the product gets changed, and in the unimolecular substitution, the stereochemistry remains the same.

The nucleophile in the nucleophilic reaction replaces the leaving group present in the substrate.

a. In the given reaction, the nucleophile is an oxide, and the leaving group is iodide. The oxide group attacks the carbon-bearing iodine bond (C-I). Therefore, the product is formed by the elimination of iodide, as shown below:

Nucleophilic substitution reaction

b. In the given reaction, the nucleophile is a terminal ethyne ion, and the leaving group is chloride. The ethyne ion attacks the carbon-bearing iodine bond (C-Cl). Therefore, the product is formed by the elimination of chloride as shown below:

Nucleophilic substitution reaction

c. In the given reaction, the nucleophile is an azide group, and the leaving group is chloride. The azide ion attacks the carbon-bearing iodine bond (C-Cl). Therefore, the product is formed by the elimination of chloride as shown below:

Nucleophilic substitution reaction

d. In the given reaction, the nucleophile is ^-SH group, and the leaving group is chloride. The ^-SH attacks at the carbon-bearing iodine bond

(C-Cl) on the backside of the plane.

Therefore, the product is formed by the elimination of chloride as shown below:

Nucleophilic substitution reaction