A qualitative description of chemical reactivity in terms of
the molecular orbitals of the reactants is offered by the perturbation molecular
orbital (PMO) theory. As per this theory, the spatial shape and the energy
aspects of the MOs of each reactant get perturbed due to approach of the
other-reactant MOs. In other words, there is a mutual perturbation of the
molecular orbitals of the reacting molecules during a reaction, the perturbation
continuing until the reaction is over and the products are formed.
The PMO theory has been successfully used to draw qualitative
conclusions about the course of some chemical reactions, worthwhile examples
being the familiar applications of the Woodward-Hoffmann rules to organic
pericyclic reactions. In pericyclic reactions involving one reactant, the
highest-energy occupied MO (HOMO) is of prime importance. Thus for thermal
cyclisation of substituted s-cis 1,3-butadiene, it is found that there occurs
conrotatory ring closure, as only conrotatory movement of the orbitals would
provide a bonding interaction between the two newly overlapping lobes of
its HOMO (whereas disrotatory movement would have provided here an
antibonding interaction).
next mukherji& singh macmillan ISBN 0333 90461 3(available in google book,,,i uploded jast search by isbn number)
page...373 electrocyclic reaction to 378
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