Vibronic coupling interactions in organic radical cations : a matrix ESR study

This dissertation is divided into four parts, each with its own independent reference section. The parts are summarized as follows. I. Principles: (1) a general discussion of radical cations in both gas and condensed phases as well as an overview of the Freon technique for observing organic radical cations by ESR, (2) basic electron spin resonance theory to first order, (3) simple perturbational theory to describe the vibronic coupling phenomenon and an example of a qualitative application of the theory to describe the proposed geometric distortion in the model ethylene radical cation. II. The Pseudo- Jahn-Teller Effect in Organic Radical Cations: (1) a vibronic coupling mechanism is used to explain why the butatriene radical cation is predicted to be distorted from planarity, based upon a vibrational analysis of the PE spectrum of butatriene as well as current ESR results which demonstrate that the magnitude of the observed coupling to the four protons exhibit a significant matrix dependency, which would seem to be indicative of a twisted structure in which the angle of twist is dependent upon environmental factors, (2) a reinvestigation of the bicyclo[2.2.2]octene radical cation system in what is believed to be the first clear-cut case of a pseudo-Jahn-Teller distortion in an organic radical cation by the experimental observation of a double minimum, as demonstrated by a reversible change in the ESR spectrum exhibiting the alternating linewidth effect, (3) the vinylidenecyclopropane radical cation is shown to be another case in which an experimentally observed double minimum demonstrates a true pseudo-Jahn-Teller effect.

III. Vibronic Coupling Interactions and Spontaneous Rearrangements: (1) the rearrangement of oxidized bicyclo[1.1.1]pentane to yield the 1,4-pentadiene radical cation can be predicted based on a vibronic coupling interaction between the two lowest energy cationic states of the parent bicyclopentane cation, with the coupling vibration becoming the reaction coordinate in a concerted process, (2) oxidation of [1.1.1]propellane is found to yield a rather novel distonic radical cation species that is possibly generated by going through a dimethylenecyclopropane radical cation intermediate (as oxidation of dimethylenecyclopropane yields the same distonic species), and its formation can be predicted by again invoking a vibronic coupling mechanism starting from either the propellane or dimethylenecyclopropane parent radical cations.IV. Experimental: the experimental methods and procedures for the completion of this research are described.