Chapter 5, Problem 5.36SP

(a)

Interpretation Introduction

To determine: The mechanism that corresponds to occurrence of free radical halogenations exclusively at the benzylic position.

Interpretation: A mechanism that corresponds to the reason as to why free radical halogenations occurred exclusively at the benzylic position is to be proposed.

Concept introduction: Free radical bromination occurs exclusively at the benzylic position. The benzylic position is next to the aromatic ring. In the first step, there is homolytic cleavage of bromine molecule. The electrons are shared equally among both the bromine atoms. Bromine abstracts the benzylic proton from the given compound to result in the formation of $\text{HBr}$ and a ${\text{sp}}^{\text{2}}$ planar benzylic carbon. The benzylic radical is resonance stablised.

(b)

Interpretation Introduction

To draw: The two stereoisomers that result from the monobromination at the benzylic position.

Interpretation: The structure of the two stereoisomers that result from the monobromination at the benzylic position is to be drawn.

Concept introduction: Stereoisomers are further divided into two categories: optical isomers and geometrical isomers. The two different forms in which a single chiral carbon can exist is referred to as enantiomers. The class of diastereomers includes stereoisomers that are not enantiomers.

(c)

Interpretation Introduction

To determine: The R and S configurations of the asymmetric carbon atoms in the product.

Interpretation: The R and S configurations to the asymmetric carbon atoms in the product are to be assigned.

Concept introduction: The enantiomers of a chiral compound can be named with the help of right hand and left hand configuration. In fisher projection, chiral carbon atom is represented by a cross. When two groups on a fisher projection are interchanged, the configuration of chiral carbon also changes from (R) to (S) or (S) to (R).

(d)

Interpretation Introduction

To determine: The relationship between the isomeric products.

Interpretation: The relationship between the isomeric products is to be stated.

Concept introduction: Stereoisomers are further divided into two categories: optical isomers and geometrical isomers. The two different forms in which a single chiral carbon can exist is referred to as enantiomers. The class of diastereomers includes stereoisomers that are not enantiomers.

(e)

Interpretation Introduction

To determine: If the products are produced in identical amounts.

Interpretation: The validation of the fact that the products are formed in equal amounts is to be stated.

Concept introduction: Stereoisomers are further divided into two categories: optical isomers and geometrical isomers. The two different forms in which a single chiral carbon can exist is referred to as enantiomers. The class of diastereomers includes stereoisomers that are not enantiomers.

(f)

Interpretation Introduction

To determine: If the products have identical physical properties.

Interpretation: The validation of the fact that the products have identical physical properties is to be stated.

Concept introduction: Stereoisomers are further divided into two categories: optical isomers and geometrical isomers. The two different forms in which a single chiral carbon can exist is referred as enantiomers. The class of diastereomers includes stereoisomers that are not enantiomers.