Chapter 14, Problem 14.4P

Interpretation Introduction

Interpretation:

Why each terminal carbon in the allyl anion ${\text{(CH}}_{\text{2}}{\text{ = CH - CH}}_{\text{2}}^{\text{-}})$ bears the same negative partial charge is to be explained using its MO picture.

Concept introduction:

The overlap of the two atomic orbitals (AOs) results in the formation of two molecular orbitals (MOs), one of which is lower in energy than the original AOs, and the other higher in energy than the original AOs. The two are called bonding MO and antibonding MO respectively. The two electrons will occupy the lower energy MO resulting in a $\text{π}$ bond. For a linear system of conjugated p orbitals, all nodal planes in the resulting $\text{π}$ MO must be positioned symmetrically about the center of that set of p orbitals.