Chapter 25, Problem 25.47P

Interpretation Introduction

Interpretation:

Why no radical bromination is observed at the ${\text{3}}^{\text{o}}$ of $\text{bicyclo [2}\text{.2}\text{.1] heptane}$ even though bromination of the ${\text{3}}^{\text{o}}$ carbon of $\text{bicyclo [3}\text{.3}\text{.1] nonane}$ is 100% is to be explained.

Concept introduction:

The probability of radical halogenation depends on the type of carbon where the substitution occurs. It increases as ${\text{1}}^{\text{o}}{\text{ < 2}}^{\text{o}}{\text{ < 3}}^{\text{o}}$, so in case of alkanes containing all three types, substitution occurs preferentially at the ${\text{3}}^{\text{o}}$ carbon. This is because the stability of the carbon radical intermediate formed in the first propagation step increases in the order ${\text{1}}^{\text{o}}{\text{ < 2}}^{\text{o}}{\text{ < 3}}^{\text{o}}$.