Phosphorus molecular orbital model

Semi-empirical molecular orbital calculations have been carried out on the model phosphorane HaPiCHa. Besides the expected transfer of charge, the inclusion of the phosphorus 2>d orbitals showed a significant hyperconjugative interaction between the CHg orbitals and a 2>d orbital of appropriate symmetry on phosphorus. Calculations on cyclopropylidene-phosphorane revealed a similar interaction between the Walsh orbitals of the ring and an in-plane phosphorus 2>d orbital. 

In 1974 Trippett (35) made the interesting observation from molecular models that the boat conformation for a six-membered ring located (a-e) in an oxyphosphorane is the most stable since it is the only one that positions the lone pair of electrons on the equatorial ring oxygen atom in the favored equatorial plane for k back-bonding to empty phosphorus d orbitals. For this requirement to be met, the dihedral angle... 

The P2 molecule contains phosphorus atoms from the third row of the periodic table. We will assume that the diatomic molecules of the Period 3 elements can be treated In a way very similar to that which we have used so far. Thus we will draw the MO diagram for P2 analogous to that for N2. The only change will be that the molecular orbitals will be formed from 35 and 2p atomic orbitals. The P2 model has 10 valence electrons (5 from each phosphorus atom). The resulting molecular orbital diagram is... 

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