Chapter 18, Problem 5PP

Interpretation Introduction

Interpretation:

The given observations are to be explained by the halogenation mechanism.

Concept Introduction:

▸ Keto and enol form of carbonyl compounds are constitutional isomers. Inter-convertible keto and enol forms are tautomer.

▸ An enol and enolates can be formed by replacing the hydrogen at the $\alpha$ carbon.

▸ The $\alpha$ hydrogen can undergo halogen substitution at the $\alpha$ carbon in the presence of an acid and a base.

▸ When halogen substitution reaction takes place in the presence of an acid it is called as acid catalyzed halogenation reaction.

▸ When halogen substitution reaction takes place in the presence of a base it is called as base prompted halogenation reaction.

▸ In the base prompted halogenation reaction and acid catalyzed halogenation reaction slows rates are independent from the concentration of the halogens.

▸ The equimolar mixture of two enantiomers are called a racemic mixture.

▸ Racemization takes place at $\alpha$ hydrogen in the presence of acids or bases.