Chapter 16.4, Problem 7PTS

Interpretation Introduction

Interpretation:

The diene which yields different products (four and two) on treating with $\text{HBr}$ should be explained.

Concept introduction:

Conjugated Dienes undergoes addition reactions with $\text{HBr}$ as similar to simple alkenes addition with $\text{HBr}$.

• The allylic carbocation is formed as an intermediate by the addition of proton in the $\text{HBr}$.
• The ${\text{Br}}^{-}$(nucleophilic) can attacks in either of the two resonance stabilized carbocation’s in the in the allylic intermediate. 

For the Butadiene derivatives, there are four carbons for addition of proton, but at C1 and C4 carbons only forms the allylic carbocation.

To explain: the given dienes yields four and two products if the dienes are treated with $\text{HBr}$.