Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

The crucial role of electron spin in the control of the reaction channels in the region of activated complexes can easily be inferred from the general principles of chemical bonding. Magnetic perturbations could change spin at the intermediate stages of a reaction or in the region of activation barriers and could hence influence the reaction rate through spin switching of the reaction paths. Spin-orbit coupling is one of the most important intrinsic magnetic perturbations in molecules; its role in chemical reactivity is here shown by a few typical examples. Spin-orbit coupling induced spin flip could also be important in catalysis by transition metals. General qualitative arguments predict great enhancements of the spin-orbit coupling in catalytic complexes with transition metal compounds. The concept of spin-catalysis is introduced in order to describe and classify a wide range of phenomena in which chemical reactions are promoted by substances assisting in inducing spin changes and overcoming spin-prohibition. This concept is based on results of quantum chemical calculations with account of spin-orbit coupling and configuration interaction in the intermediate complexes. Besides spin-orbit coupling, the role of intermolecular exchange interaction with open shell catalysts is stressed. The catalytic action would definitely depend on the efficiency of spin uncoupling inside the reacting substrate molecule and this could be induced by magnetic and exchange perturbations.