Highest occupied molecular structural analysis

Molecular orbital calculations have been performed on compounds 19 and 20 . The calculated PM3 equilibrium geometric structures show that these compounds are severely distorted from planarity in accordance with X-ray structural analysis (see Section 8.I2.3.I). On the other hand, PM3 calculations performed on both neutral and oxidized/reduced compounds show that oxidation and reduction induce a clear gain of aromaticity. Predictions using the nonempirical valence effective Hamiltonian (VEH) method have shown that the electronic charge density in the highest occupied molecular orbital (HOMO) is localized on the benzodithiin 19 or benzoxathiin 20 rings. 

Acrylonitrile appears to coordinate to transition metal ions primarily through its carbon-carbon double bond (highest occupied molecular orbital of that molecule96 ). This mode of coordination has been deduced from the absence of the stretching frequency nc=c97 and, in the cases of Fe(CO)4(CH2=C-CN)98 and Ni(PR.3)2(CH2=CH—CN)99, confirmed by X-ray structural analysis. The CN bond of the acrylonitrile ligand is slightly weakened in these complexes, as shown in a small increase of the bond length and decrease of t>cN-... 

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