Chapter D, Problem D.6P

Interpretation Introduction

Interpretation:

The approach of the ${\text{Br}}^{\text{-}}$ on the ${{\text{(CH}}_{\text{3}}\text{)}}_{\text{3}}{\text{C}}^{\text{+}}$ carbocation from within the plane of the central C atom in the coordination step is to be discussed.

Concept introduction:

In the coordination step, a substrate undergoes substitution, in which the nucleophile is attached to the electrophile. The conjugate bases of strong acids act as nucleophiles. The negative charged nucleophile is attracted to an atom bearing a positive charge on the electrophile. However, for the bond formation between a nucleophile and an electrophile, only a single covalent bond is formed. Nucleophile is the electron rich species, and it will contribute the HOMO interaction, and electron poor C atom will contribute the LUMO interaction. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) must have axial overlap or parallel overlap. The axial overlap between HOMO and LUMO has substantial net overlap, so this reaction is allowed. If the HOMO and LUMO do not have a substantial overlap, this overlap is forbidden.