Chapter D, Problem D.4P

Interpretation Introduction

Interpretation:

It is to be determined whether the proton transfer between ${\text{OH}}^{-}$ and $\text{HCl}$ is allowed if ${\text{OH}}^{-}$ were to approach $\text{HCl}$ from the same end as $\text{Cl}$. Whether you would expect that elementary step to take place or not is to be justified.

Concept introduction:

An elementary step in which a proton is transferred from an electron-poor site to an electron-rich site and one bond is broken and another is formed simultaneously is called proton transfer step.

In an elementary step, the flow of electrons is from an electron rich group to an electron poor atom. 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 reaction is forbidden.