Chapter 16, Problem 37PP

Interpretation Introduction

Interpretation:

For the 2-ethyl-3-methyl-1,3-cyclohexadiene treated with $\text{HBr}$, the four products and the mechanism that explains the formation of each product are needed to be drawn.

Concept introduction:

Conjugated Dienes undergoes addition reactions with $\text{HBr}$ as similar to simple alkenes addition with $\text{HBr}$, but instead of single carbocation intermediate formation of simple alkenes; dienes will form resonance stabilized allylic carbocation as an intermediate.

• 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 type dienes, there are four carbons for addition of proton, but at C1 and C4 carbons only forms the allylic carbocation.

To draw: the four products and the mechanism that explains the formation of each product for the 2-ethyl-3-methyl-1,3-cyclohexadiene treated with $\text{HBr}$.