Chapter 10.6, Problem 23E

(a)

Interpretation Introduction

Interpretation: The structure of the stereoisomers expected from the reaction of bromine with $\text{1-methylcyclohexene}$ should be drawn.

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 results 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.

In accordance with Cahn-Ingold-Prelog rules; if two high priority substituents happen to appear on opposite sides of olefinic bond then the absolute configuration for the alkene will be would be “E”.

(b)

Interpretation Introduction

Interpretation: Whether the stereochemistry of products drawn like or unlike should be identified.

Concept introduction:In order to assign absolute configuration of R and S, Cahn − Ingold − Prelog rules are used and the first step is to assign the priority order with the atomic number as the fundamental property. The one with the highest atomic number gest highest priority and is designated as “1” and so on.

In order to distinguish the relative stereochemistry of two chiral centers situated adjacent to one another, like or unlike notation is used.

For enantiomeric pairs that have same stereochemistry at adjacent carbon atoms, the notation “l” is designate “like” and notation “u” is designate “un-like”.