Comments on two treatments of symmetry rules in chemical reactions

In this paper we compare a recently presented approach to the determination of symmetry rules for chemical reactions based on adiabatic electronic states to earlier work in which a quasiadiabatic representation was used. The adiabatic approach is shown not to lead directly to Woodward-Hoffmann symmetry rules, and a number of the conclusions of the adiabatic work are shown to be incorrect and inconsistent. An indirect approach for deriving the Woodward-Hoffman rules in the adiabatic representation is presented which uses the connection between the adiabatic and quasiadiabatic representations to relate barrier height to the quasiadiabatic electronic matrix elements.