Our interests are in the area of physical-organic chemistry . Here, we attempt to understand the behavior and reactions of molecules using a combination of experimental and theoretical approaches. Current research areas include:

1. Studies of conformational equilibria and solvent effects on these equilibria. We have recently examined the axial-equatorial ratios for alkylcyclohexanes (experiment and theory), the mono and dihalocyclohexanes, and phenyl and 1-phenyl-1-methylcyclohexane. We are particularly interested in cases in which the axial forms are preferred at equilibrium, and we are studying several of these systems in order to determine the origin of the axial preference.

2. Studies of NMR chemical shifts. We have developed a procedure for obtaining NMR shielding on an MO basis from ab initio calculations, and also to obtained the occupied-virtual coupling components of the paramagnetic shielding. This has been applied to a number of types of organic compounds with considerable success, and further systems are presently being studied. The tensor components of the shielding also are being measured via static solid state NMR spectroscopy.

3. Studies of the effect of geometrical distortion on the properties of organic compounds. We have recently studied spiropentyl derivatives in some detail, both with regard to the effects of introducing a bridge which will tend to twist the cyclopropane rings toward each other, and with the cations that are formed in the deamination of spiropentylamine and the solvolysis of spiropentyl derivatives. Other studies are concerned with the effect of fluorine substitution on the stability of small ring cycloalkynes.

4. Studies of solvent effects on reactions. Solvents often play an important role in determining the rates and products of reactions. We have developed a reaction field model for studying these effects and have applied it with considerable success to a variety of reactions, including the Menshutkin reaction.
Besides the reaction field studies, we also make use of discrete solvent molecules. An example is the reaction of organolithium compounds with organic halides, forming Ate complex intermediates or transition states. We have shown that the stability of the Ate complex can be increased both by complexing the lithium cation, and by the introduction of electronegative groups.

5. Studies of electronically excited states of molecules. Many photochemical reactions are known, including those that occur in the upper atmosphere. A prerequisite for studying these reactions is a good understanding of the electronically excited states of the molecules of interest. We have a 1 M vacuum ultraviolet spectrometer that allows us to obtain experimental data, and we have considerable experience in the calculation of the transition energies, and in interpreting the results of the calculations in terms of shifts in electron density.

Please send comments or questions to Kenneth.Wiberg@yale.edu

 Last updated August 21, 1999