Chapter 2, Problem 61P

(a)

Interpretation Introduction

Interpretation: Bond-line structures for reaction 1 and 2 should be formulated.

Concept introduction: Bimolecular substitution or ${\text{S}}_{\text{N}}2$ proceeds via single-step mechanism. Thus it is well known as concerted mechanism. Nucleophile approaches carbon while the leaving group still departs from the rear side (opposite to leaving group). The transition state only illustrates the geometric orientation of the substrates and reagents as they pass through the maxima in the single-step mechanism.

${\text{S}}_{\text{N}}2$ pathway as it is a stereospecific reaction. This essentially means the R stereoisomer can only lead to inverted S stereoisomer and vice versa. Thus the outcome is the rear side displacement of leaving group.

(b)

Interpretation Introduction

Interpretation: The nature of carbon at reactive site of the starting haloalkane should be identified.

Concept introduction:The carbon linked to one alkyl/carbon while other two $\text{H}$ are termed primary carbon. Thus hydrogen linked to such carbon is referred as primary.

The carbon linked to two alkyl /carbons and one $\text{H}$ is termed secondary carbon. Thus hydrogen linked to such carbon is referred as secondary.

The carbon linked to three alkyl groups/carbons and no $\text{H}$ is termed tertiary carbon. Thus hydrogen linked to such carbon is referred as tertiary.

(c)

Interpretation Introduction

Interpretation:The manner in that different species would react and possible pathway that describes difference in rate between the reactions should be determined.

Concept introduction: Bimolecular substitution or ${\text{S}}_{\text{N}}2$ proceeds via single -step mechanism. Thus it is well known as concerted mechanism. Nucleophile approaches carbon while the leaving group still departs from the rear side (opposite to leaving group). The transition state only illustrates the geometric orientation of the substrates and reagents as they pass through the maxima in the single-step mechanism.

${\text{S}}_{\text{N}}2$ pathway as it is a stereospecific reaction. This essentially means the R stereoisomer can only lead to inverted S stereoisomer and vice versa. Thus the outcome is the rear side displacement of leaving group.

(d)

Interpretation Introduction

Interpretation: Hashed-wedged line structures to make a three-dimensional pathway to describe the trajectory should be drawn.

Concept introduction: Bimolecular substitution or ${\text{S}}_{\text{N}}2$ proceeds via single -step mechanism. Thus it is well known as concerted mechanism. Nucleophile approaches carbon while the leaving group still departs from the rear side (opposite to leaving group). The transition state only illustrates the geometric orientation of the substrates and reagents as they pass through the maxima in the single-step mechanism.

A general ${\text{S}}_{\text{N}}2$reaction mechanistic pathway is illustrated below:

  

${\text{S}}_{\text{N}}2$ pathway as it is a stereospecific reaction. This essentially means the R stereoisomer can only lead to inverted S stereoisomer and vice versa. Thus the outcome is the rear side displacement of leaving group.

Polar-aprotic solvents accelerate the rate of ${\text{S}}_{\text{N}}2$ reactions. These solvents possess partial positive and negative charges also. However, they do not liberate any proton to the substrate unlike water, methanol solvents. Acetone, DMSO, THF or DMF are categorized as polar aprotic solvent.