Chapter 5, Problem 62P

(a)

Interpretation Introduction

Interpretation:Numbers of possible stereoisomeric products formed in the monobromination of racemic $\text{trans-1,2-dimethylcyclohexane}$ should be determined.

Concept introduction:Halogenation products are governed by the achirality or already present stereocenter in the molecule.

If the halogenation occurs at the chiral center of the substrate it results in a racemic mixture. This is attributed to formation of achiral radical intermediate that can be attacked equally from the top face or bottom face. Thus two enantiomers R and S are formed in equal amount that makes the overall mixture optically inactive.

If the halogenation occurs at one of the two chiral centers of the substrate it results in change in absolute configuration at only one of the stereocenter and thus diastereoisomer result. These diastereomers are formed in unequal amounts.

(b)

Interpretation Introduction

Interpretation: Numbers of possible stereoisomeric products formed in the monobromination of racemic $\left(R,R\right)\text{-1,2-dimethylcyclohexane}$ should be determined.

Concept introduction:Halogenation products are governed by the achirality or already present stereocenter in the molecule.

If the halogenation occurs at the chiral center of the substrate it results in a racemic mixture. This is attributed to formation of achiral radical intermediate that can be attacked equally from the top face or bottom face. Thus two enantiomers R and S are formed in equal amount that makes the overall mixture optically inactive.

If the halogenation occurs at one of the two chiral centers of the substrate it results in change in absolute configuration at only one of the stereocenter and thus diastereoisomer result. These diastereomers are formed in unequal amounts.

(c)

Interpretation Introduction

Interpretation:Whether the various stereoisomeric products obtained from monobromination of racemic $\text{trans-1,2-dimethylcyclohexane}$ and $\left(R,R\right)\text{-1,2-dimethylcyclohexane}$ cannot be separated on the basis of physical properties or not should be indicated.

Concept introduction:Halogenation products are governed by the achirality or already present stereocenter in the molecule.

If the halogenation occurs at the chiral center of the substrate it results in a racemic mixture. This is attributed to formation of achiral radical intermediate that can be attacked equally from the top face or bottom face. Thus two enantiomers R and S are formed in equal amount that makes the overall mixture optically inactive.

If the halogenation occurs at one of the two chiral centers of the substrate it results in change in absolute configuration at only one of the stereocenter and thus diastereoisomer result. These diastereomers are formed in unequal amounts.