Theory of Nonbonded Interactions

While physical chemists have focused attention primarily upon van der Waals interactions in their attempts to understand why molecules or molecular fragments attract or repel each other, we have taken the position that much can be learned with regards to the role of nonbonded interactions in chemistry within the framework of one determinental MO theory. In other words, we have tried to convey the message that the answer to why chemical entities attract or repel each other may be obtained by reference to a fundamental bonding theory like OEMO theory. In this section, we develop a theory of nonbonded interactions from that standpoint. 

Our discussion in this and certain subsequent sections will involve torsional isomerism. In such cases, we can use Eqs. (1) to (6) where Hy is approximated by kSjj. Accordingly, the aforementioned equations become  

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