Variable hybridisation - a simple model of covalent bonding
Extensive evidence is presented which conclusively shows that variable hybridisation is a simple, pictorial and very useful model of covalent bonding. The noninteger hybridisation parameters calculated by the iterative maximum overlap approach are very rich in chemical information. They can be successfully correlated with a number of physico-chemical gross molecular properties which encompass heats of formation, heats of hydrogenation, strain energies etc. They reflect also local properties like spin-spin coupling constants across one bond, C-H stretching frequencies, thermodynamic proton acidities, intrinsic bond energies etc. In addition, the iterative version of the maximum overlap method provides quite reliable estimates of molecular shapes and sizes. Properties which are completely determined by molecular geometry such as diamagnetic contributions to the magnetic susceptibility and nuclear magnetic shielding are well reproduced being in nice agreement with experimental data and rigorous ab initio results.