Chapter 6, Problem 40P

(a)

Interpretation Introduction

Interpretation:The rate constant for reaction between ${\text{CH}}_{\text{3}}\text{Cl}$ and $\text{KSCN}$ should be calculated.

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.

Bimolecular substitution reaction depend concentration of both the alkyl halide and nucleophile. Hence the name ${\text{S}}_{\text{N}}2$ is abbreviated to indicate second order dependence of this substitution.

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.

(a)

Interpretation Introduction

Interpretation:The initial rates for reaction between ${\text{CH}}_{\text{3}}\text{Cl}$ and $\text{KSCN}$ with indicated three initial reactant concentrations sets should be calculated.

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:

  

Bimolecular substitution reaction depend concentration of both the alkyl halide and nucleophile. Hence the name ${\text{S}}_{\text{N}}2$ is abbreviated to indicate second order dependence of this substitution.