Qualitative molecular orbital theory QMOT

To create group orbitals or delocalized molecular orbitals, we need to understand how to combine atomic orbitals properly. Therefore, the starting point in developing our second model of organic bonding is a set of rules that lead by inspection to group orbitals and molec-ular orbitals. This procedure is called qualitative molecular orbital theory (QMOT). 

Ab initio and semiempirical computational methods have proved extremely useful. But also needed is a simple conceptual scheme that enables one to predict the broad outlines of a calculation in advance, or else to rationalize a coii5)uted result in a fairly simple way. Chemistry requires conceptual schemes, simple enough to carry around in one s head, with which new information can be evaluated and related to other information. Such a theory has developed alongside the mathematical methods described in earlier chapters. We shall refer to it as qualitative molecular orbital theory (QMOT). In this chapter we describe selected aspects of this many-faceted subject and illustrate QMOT applications to questions of molecular shape and conformation, and reaction stereochemistry. 

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