Problem on Elimination Vs Substitution

Description:

Problem

Justify the given reactions −

R − Cl + aq.KOH → R − OH

R − Cl + alc.KOH → alkene

Solution

Let the alkyl halide be CH₃CH₂Cl

The nucleophile in the above reaction condition is OH⁻ (in aqueous medium).

Under alcoholic conditions,  the nucleophile is EtO⁻ which is bulkier than OH⁻.

It would prefer to act as a base and abstract hydrogen rather than act as a nucleophile and attack the alkyl halide.

This results in elimination and not substitution.