Chapter 6, Problem 49P

Interpretation Introduction

Interpretation:

The LUMO in ${\text{S}}_{\text{N}}\text{1}$ reaction is to be explained and in which reactant and species the LUMO is found is to be determined. The lobe of the LUMO in the Isopropyl Methyl Ether Carbocation model with which a nucleophile would interact is to be identified. The reason behind the large orbital lobe between the oxygen and the carbon of the carbocation is to be explained.

Concept Introduction:

▸ 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:

▸ ${\text{3}}^{\text{o}}\text{carbocation}\text{>}{\text{2}}^{\text{o}}\text{carbocation}{\text{>1}}^{\text{o}}\text{carbocation}\text{>methyl}\text{carbocation}$

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

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