Chapter 14, Problem 14.3YT

Interpretation Introduction

Interpretation:

For the given MO diagram of $\text{buta-1, 3-diene}$, all regions that give rise to bonding contributions and all regions that give rise to antibonding contributions are to be labeled.

Concept introduction:

The MO arises from interacting p AOs of two atoms. MO energies differ as a result of constructive and destructive interference among contributing AOs. Each pair of overlapping AOs with the same phase lowers the MO energy and corresponds to a bonding interaction in an MO while each pair of overlapping AOs with the opposite phases raises the MO energy and corresponds to an antibonding interaction in an MO. The destructive interference gives rise to a nodal plane. The contributions of the AOs to produce a bonding, nonbonding, or antibonding MO depend on the net interaction.  In the MO diagram, only $\text{π}$ electrons are considered. In the case of a conjugated system, number of $\text{π}$ electrons corresponds to p orbitals which are considered atomic orbitals (AOs) in the MO diagram. For conjugated alkenes, there are also equal numbers of bonding and antibonding orbitals. The bonding interaction results from adjacent p orbitals which are in the same phase, and when the adjacent orbital in opposite phase results in antibonding interaction, it is also represented by a nodal plane.