Chapter 21, Problem 36P

Interpretation Introduction

Interpretation:

The contradictory trend of halogens as leaving group in the substitution reactions is to be explained.

Concept introduction:

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

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

Free radical is an atom, molecule, or ion that has unpaired electrons, which makes it highly chemically reactive.

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.

Elimination reaction: A reaction in which two substituent groups are detached and a double bond is formed is called elimination reaction.

Addition reaction: It is the reaction in which unsaturated bonds are converted to saturated molecules by the addition of molecules.

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.

${\text{S}}_{\text{N}}1$ is a unimolecular substitution reaction, and is also called a nucleophilic substitution reaction. The reaction takes place in the polar protic solvent.

In ${\text{S}}_{\text{N}}1$ reaction, the formation of carbocation takes place. ${\text{S}}_{\text{N}}1$ reaction gives two products. One is retention of stereochemistry, and the other is inversion of stereochemistry.

${\text{S}}_{\text{N}}2$ is a bimolecular substitution reaction, and is also called a nucleophilic substitution reaction. The order of the reaction is 2.

In ${\text{S}}_{\text{N}}2$ reaction, one bond is broken and one bond is formed. In ${\text{S}}_{\text{N}}\text{2}$ reaction, the nucleophile attacks on less steric hindrance carbon. ${\text{S}}_{\text{N}}2$ reaction gives inversion. The reaction takes place in the polar aprotic solvent.

${\text{S}}_{\text{N}}\text{2}$ 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.

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