Chapter 25, Problem 25.22YT

Interpretation Introduction

Interpretation:

The diagram in Figure 25-13 is to be studied and the initiation and propagation steps are to be matched to Equation 25-33a, 25-33b, 25-33c, or 25-33d.

Concept introduction:

A hydrogen halide adds across the double bond of an alkene in a Markovnikov fashion under normal conditions. ${\text{H}}^{\text{+}}$ adds to the less alkyl-substituted $\text{C}$ atom whereas the halide anion adds to the more alkyl-substituted $\text{C}$ atom. The reason is that the first step of the mechanism is protonation of the $\text{C=C}$ double bond, which proceeds to give the more stable carbocation intermediate. If a small amount of peroxide ($\text{RO-OR}$) is present, however, then the major product is produced according to anti-Markovnikov addition. The $\text{H}$ atom adds to the more substituted $\text{C}$, and the halide atom adds to the less substituted one. Peroxides are radical initiators because they contain a weak $\text{O-O}$ bond. Hence, the reaction in Equation 25-32 proceeds by radical mechanism. The whole mechanism for Equation 25-32 is given in Equation 25-33a, 25-33b, 25-33c, or 25-33d.