Class 12 Chemistry - Chapter Haloalkanes and Haloarenes NCERT Solutions | The treatment of alkyl chlorides with aq

Welcome to the NCERT Solutions for Class 12th Chemistry - Chapter Haloalkanes and Haloarenes. This page offers a step-by-step solution to the specific question from Exercise 2, Question 20: the treatment of alkyl chlorides with aqueous koh....
Question 20

The treatment of alkyl chlorides with aqueous KOH leads to the formation of alcohols but in the presence of alcoholic KOH, alkenes are major products. Explain.

Answer

In an aqueous solution, KOH almost completely ionizes to give OH - ions. OH - ion is a strong nucleophile, which leads the alkyl chloride to undergo a substitution reaction to form alcohol.

On the other hand, an alcoholic solution of KOH contains alkoxide (RO - ) ion, which is a strong base. Thus, it can abstract a hydrogen from the β-carbon of the alkyl chloride and form an alkene by eliminating a molecule of HCl.

OH - ion is a much weaker base than RO - ion. Also, OH - ion is highly solvated in an aqueous solution and as a result, the basic character of OH - ion decreases. Therefore, it cannot abstract a hydrogen from the β-carbon.

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