Chapter 18.2, Problem 6P

Interpretation Introduction

a) Bromobenzene, 2-bromopropane, bromoethane

Interpretation:

The compounds bromoethane, 2-bromopropane and bromobenzene are to be ranked in the order of their reactivity in Williamson synthesis.

Concept introduction:

In Williamson synthesis, the primary alkyl halides are preferred as the reaction occurs through a S_N² mechanism. With secondary and tertiary alkyl halides elimination occurs through E² mechanism to yield alkenes. Aromatic halides are less reactive than aliphatic halides.

To rank:

The compounds bromoethane, 2-bromopropane and bromobenzene in the order of their reactivity in Williamson synthesis.

Interpretation Introduction

b) Chloroethane, bromoethane, 1-Iodopropene

Interpretation:

The compounds chloroethane, bromoethane and 1-iodopropene are to be ranked in the order of their reactivity in Williamson synthesis.

Concept introduction:

In Williamson synthesis, te alkoxuide reacts with primary alkyl halides through a S_N² mechanism. The requirements are thus a backside attack, a stronger nucleophile and a better leaving group. Among the halides, iodine is better leaving than bromine which in turn is a better leaving than chlorine. Vinyl halides are less reactive than alkyl halides.

To rank:

The compounds chloroethane, bromoethane and 1-iodopropene in the order of their reactivity in Williamson synthesis.