Excited State Reactions

The analysis of the fragmentation of tetramethyl-1,2-dioxetane at the end of the preceding chapter, in which three competing processes had to be considered, foreshadows the difficulty of applying the criteria of symmetry conservation to the much more complex reactions that originate in an excited state of the reactant. An attempt will nevertheless be made in the following sections to show how the approach developed in the preceding chapters can be extended to deal with them. Each of the photochemical reactions chosen for discussion was selected in order to illustrate as convincingly as possible a particular point that has to be kept in mind when applying symmetry criteria to excited state reactions. In no case is it claimed that the mechanistic analysis is conclusive.