Our current research efforts are focused on four areas of physical organic chemistry: the study of electron transfer by dynamic NMR spectroscopy, Mobius aromatic molecules, highly reactive molecules and applications of molecular orbital theory. Our theoretical interests are, in general, closely linked to problems in the first three areas.
We are currently synthesizing a series of compounds with two cyclooctatetraene rings bridged by various saturated and unsaturated groups. The dynamical processes of bond switching and electron transfer in the dianions of these molecules arc being studied by dynamic C-13 NMR spectroscopy in order to determine the mechanisms of charge transfer and the relative conductivities of the bridging groups. Detailed studies of the structures of ion pairs of carbanions using C-13 NMR spectroscopy and ab initio molecular orbital calculations are also underway.
Mobius molecules are molecules with a helical array of orbitals possessing an odd number of inversions of orbital phase in the basis set of orbitals. Such molecules are predicted to be aromatic if they possess 4n (i.e., 4, 8, 12, etc.) delocalized electrons. No unambiguous examples of such molecules have been identified. We are currently synthesizing various substituted trans-bicyclo[6.1.0]nona- 2,4,6-trienes and determining their structures by X-ray crystallography in order to obtain evidence for Mobius aromaticity. These molecules undergo a novel sigmatropic rearrangement near room temperature and the mechanism of this process is also under investigation.
The synthesis and isolation of theoretically interesting and highly reactive molecules is another area of current interest. A collaborative project with colleagues in Physics and Materials Science involves the synthesis and study of new fullerene molecules ("buckyballs"). Highly reactive molecules are also being generated by the technique of vacuum gas-phase dehydrohalogenation which involves reaction with a reagent on a solid support. The reactive products are protected by generation in a partial vacuum and can be studied by direct introduction into various spectrometers. Techniques that have been employed include photoelectron, microwave and electron transmission spectroscopy.
Finally, theoretical problems currently under investigation include the accurate calculation of molecular dipole moments, C-13 NMR chemical shifts, molecular structures and electronic absorption spectra by molecular orbital calculations that incorporate the effects of electron correlation. The exceptional strength of the Department of Chemistry in computers and NMR spectroscopy is a great advantage in conducting the research described above.