Chapter 11, Problem 16PP

Interpretation Introduction

Interpretation:

The mechanisms of given reactions involved in cleavage of ethers by hydrogen iodide are to be explained.

Concept introduction:

Electrophiles are electron deficient species that have positive or partially positive charge. Lewis acids are electrophiles that accept electron pair.

Nucleophiles are electron rich species that have 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.

${\text{S}}_{\text{N}}\text{2}$ 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: ${\text{3}}^{\text{o}}\text{carbocation}\text{>}{\text{2}}^{\text{o}}\text{carbocation}{\text{>1}}^{\text{o}}\text{carbocation}\text{>methyl}\text{carbocation}$

Ethers can be cleaved by hydrogen halides like $\text{HCl, HBr, and HI}\text{.}$ Hydrogen iodides react with ethers to form alcohol and alkyl iodide. In case of unsymmetrical ethers, the mechanism governs which alkyl would form iodide. If primary and secondary alkyl groups are involved, ${\text{S}}_{\text{N}}\text{2}$ mechanism takes place and the primary alkyl forms iodide. If any of the alkyl groups is tertiary, ${\text{S}}_{\text{N}}\text{1}$ reaction takes place and the tertiary alkyl forms iodide.