Chapter 6, Problem 38P

Interpretation Introduction

Interpretation:

The formation of ${\text{RNO}}_{\text{2}}$ and $\text{RONO}$ by the reaction of $1^{\circ }$ alkyl halides with nitrite salts is to be explained.

Concept introduction:

▸ In haloalkanes, the bond between carbon and halogen is polarized by virtue of the higher electronegativity of halogen compared to carbon, which is electrophilic in nature. The replacement of halogen in haloalkanes by a nucleophile through a substitution reaction is called a nucleophilic substitution reaction.

▸ ${\text{S}}_{\text{N}}1$ is a unimolecular reaction with first-order kinetics and ${\text{S}}_{\text{N}}2$ is a bimolecular reaction with second-order kinetics.

▸ Electrophiles are electron deficient species which has positive or partially positive charge. Lewis acids are electrophiles which accept electron pair.

▸ Nucleophiles are electron rich species which has negative or partially negative charge. Lewis bases are nucleophiles which donate electron pair.

▸ Substitution reaction: A reaction in which one of the hydrogen atoms of a hydrocarbon or a functional group is substituted by any other functional group is called substitution reaction.

▸ Nucleophilic substitution reaction is a reaction in which an electron rich nucleophile attacks the positive or partial positive charge of an atom or a group of atoms to replace a leaving group.

▸ ${\text{S}}_{\text{N}}\text{2}$ reaction is the nucleophilic substitution reaction in which the two components are involved in the rate determining step.

▸ The ${\text{S}}_{\text{N}}\text{2}$ mechanism of substitution reaction occurs in secondary alkyl halides with an inversion of configuration.

▸ The ${\text{S}}_{\text{N}}\text{2}$ reaction takes place in one step. The nucleophile attacks the alkyl halide from the side opposite to the leaving group, resulting in an inversion of configuration.

▸ An ${\text{S}}_{\text{N}}1$ reaction is a nucleophilic substitution reaction in which only one component is involved in the rate-determining step.

▸ The nucleophilic substitutions in which a nucleophile replaces a leaving group are known as ${\text{S}}_{\text{N}}1$ reactions.

▸ ${\text{S}}_{\text{N}}1$ reactions are unimolecular as the rate of reaction is dependent on the concentration of a single reactant.

▸ Carbocation is a molecule having a carbon atom bearing three bonds and a positive formal charge.

▸ Carbocation are generally unstable because they do not have eight electrons to satisfy the octet rule.

▸ The order of stability of carbocation is such that the tertiary carbocation is the most stable whereas the primary carbocation is the least stable, and secondary carbocation lies between primary and tertiary carbocations.

▸ If primary carbocation is obtained in product, it rearranges itself to secondary or tertiary carbocation to form more stable product.

▸ If secondary carbocation is obtained in product, it rearranges itself to tertiary carbocation to form more stable product.

▸ The stability of carbocation: ${\text{3}}^{\text{o}}\text{carbocation}\text{>}{\text{2}}^{\text{o}}\text{carbocation}{\text{>1}}^{\text{o}}\text{carbocation}\text{>methyl}\text{carbocation}$

▸ The nucleophile which can attack a substrate through two possible sites is termed as an ambident nucleophile.

▸ Nitrite is an ambident nucleophile, which can attack a substrate through oxygen and nitrogen.