Chapter 14, Problem 14.28P

Interpretation Introduction

Interpretation:

The two-center orbital picture that describes each of the two weak resonance contributors of $\text{1, 3-butadiene}$ is to be drawn.

Concept introduction:

Overlap of atomic orbitals (AOs) can be thought of as wave interference. It can be constructive or destructive. Constructive interference increases the electron density between the two nuclei (an antinode) and results in a molecular orbital (MO) of lower energy. The phases of the overlapping orbitals are the same in this case. Destructive interference reduces the electron density between the two nuclei and results in an MO of higher energy. The phases of such AOs are the opposite. Since the electron density between the two nuclei decreases, there is a node (or a nodal plane) between the two atoms.

$\text{π}$ MOs sometimes extend over three or more atoms. In this case, different combinations of constructive and destructive interference are possible. The overall bonding character and the energy depend on the number of nodes and antinodes. If there are more antinodes than nodes, the overall interaction is bonding, and energy is lowered. If there are more nodes than antinodes, the overall interaction is antibonding, and energy increases.