James Rawles

"A Study of Variously Substituted Silyl Styrene Radical Anions by Electron Spin Resonance Spectroscopy

Electron spin resonance (ESR) spectroscopy is an analytical technique used to study the electronic structure and molecular orbital arrangement and geometry by observing unpaired electrons within a molecule. Unpaired electrons have a non-zero spin angular momentum and thus exhibit two energy levels when placed in a strong magnetic field it is this principle on which ESR is based. In a typical ESR experiment, a sample is irradiated with microwave radiation of a constant frequency while the magnetic field is swept over a predetermined range. Radicals in different molecular environments will absorb the radiation at different magnetic field strengths unique to that particular environment and through this an absorbance spectrum can be generated indicating the discreet energy absorptions within the molecule which in turn can be interpreted to divulge details about the molecular and electronic structure of the compound. In this work, ESR spectroscopy is utilized to study the molecular orbital structures of trans-beta-trimethylsilyl styrene, cis-beta-methyl-trans-beta-trimethylsilyl styrene and para-methyl-trans-beta-trimethylsilyl styrene. Particularly, the molecular orbitals surrounding the silicon atom were of interest. Coupling constants for all three molecules were measured experimentally as well as calculated using density Functional Theory. It was shown that despite siliconís lack of p orbital pi interaction, electron density was seen on both the silylmethyl hydrogens and the styrene hydrogens indicating a mechanism for electron travel across the silicon. It is proposed that the unfilled silicon d orbitals contribute to the lowest unoccupied molecular orbital wavefunction to allow the electron transfer between the silylmethyl hydrogens and the styrene backbone.