Chapter 25, Problem 25.18P

Interpretation Introduction

Interpretation:

The major product of the given reaction is to be predicted.

Concept introduction:

In radical halogenation reactions, N-bromosuccinimide (NBS) is the source of a low, steady concentration of ${\text{Br}}_{\text{2}}$. Step 1 is the homolysis of the N - Br bond to produce $\text{Br}·$$\text{Br}·$. This step requires only modest heating because the $\text{N-Br}$ bond is particularly weak. In Step 2, the newly formed $\text{Br}·$ abstracts an H atom from $\text{H-Br}$, producing HBr, a strong acid. In Step 3, therefore, a carbonyl O on NBS is protonated, which also produces ${\text{Br}}^{\text{-}}$, a strong nucleophile. Finally, Step 4 is an ${\text{S}}_{\text{H}}\text{2}$ step, in which the ${\text{Br}}^{\text{-}}$ nucleophile attacks a Br atom from a second molecule of NBS, yielding ${\text{Br}}_{\text{2}}$. This ${\text{Br}}_{\text{2}}$ further gives a radical bromination product.