Chapter 11, Problem 11.46P

Interpretation Introduction

Interpretation:

The addition of $\text{HBr}$ to $\text{buta-1, 3-diene}$ results in 1, 2-addition at cold temperatures and 1, 4-addition at warm temperatures. If the 1, 2-adduct is first formed at cold temperatures and then warmed up, the 1, 4-adduct is formed, as shown. A mechanism for this isomerization reaction is to be drawn.

Concept introduction:

At high temperatures, electrophilic addition to a conjugated diene takes place under thermodynamic control, so the major product is the one that is lowest in energy. The 1, 4-adduct must be a thermodynamic product, and the 1, 2-adduct must be a kinetic product.