Chapter 10.6, Problem 13E

Interpretation Introduction

Interpretation:The number of chiral centers present in the bromonium ion and isomeric carbocation intermediate formed during addition of bromine to $\left(\text{E}\right)\text{-stilbene}$ should be given.

Concept introduction:Alkenes are considered electron-rich and undergo bromination addition reaction with ${\text{Br}}_2$ in presence of ${\text{CCl}}_{\text{4}}$ by electrophilic addition reaction.

The mechanism of ${\text{Br}}_2$ addition occurs in two steps. In the first step, nucleophilic olefin abstracts the electrophilic bromine atom from ${\text{Br}}_2$ and this result in attack of ${\text{Br}}^{+}$ on the electron-rich olefinic bond that forms a sigma bond to each end of the olefinic bond. Such interaction leads to a three-membered bromonium ion intermediate.

In the second step, the strained bromonium ion intermediate opens while ${\text{Br}}^{-}$ attack from behind the electron-deficient carbon analogous to ${\text{S}}_{\text{N}}\text{2}$ attack.

Chiral carbon is any stereocenter attached to four different alkyl substituents. If any two of the substituent happen to be similar the center is regarded as achiral.