We describe several improvements to the reaction field model for the ab initio determination of solvation effects. First, the simple spherical cavity model is expanded to include higher-order electrostatic interactions. Second, two new and efficient implementations of the polarizable continuum model (PCM) are described, which allow a more realistic specification of the solute cavity as well as infinite-order electrostatics. Electron correlation effects are evaluated using the B3LYP density functional and Möller−Plesset perturbation theory to second order. An assessment of the importance of these various factors is made by comparing theoretical results to the experimentally known conformational equilibrium between syn and anti forms of furfuraldehyde and the C−C rotational barrier of (2-nitrovinyl)amine. Comparisons are also made with calculations that employ an ellipsoidal cavity with sixth-order electrostatics. Optimization using a simple Onsager model appears to be sufficient to evaluate the important geometry changes in solution. Energies obtained from the spherical and ellipsoidal cavity models often exhibit poor convergence in the truncated electrostatic series. Correlation to experiment is much improved when an infinite-order PCM method is used.

The reactions of tricyclo[4.1.0.01,3]heptan-4-one (5) and two related systems with diazomethane and m-CPBA were examined in order to determine the relative reactivity and migratory aptitudes for the three compounds. The reactions of 5 with diazomethane and m-CPBA yielded new derivatives of the tricyclo[5.1.0.01,3]octane ring system that showed that migration of cyclopropylcarbinyl is favored over cyclopropyl migration in this system. Photolysis of 5-diazotricyclo[4.1.0.01,3]heptan-4-one (23) in methanol and dimethylamine did not lead to ring contraction to the tricyclo[3.1.0.01,3]hexane ring system, but an interesting product was derived from an unusual rearrangement process in the photolysis in dimethylamine. Matrix photolysis of 23 at 15 K gave a decrease in the diazo band at 2085 cm-1 and the appearance of a new band at 2117 cm-1, which is a normal position expected for a small-ring ketene such as cyclopropylketene. Thus, matrix photolysis appears to have yielded a derivative of the previously unknown tricyclo[3.1.0.01,3]hexane ring system. The lithium enolate of 5 was characterized by NMR spectroscopy at −80 °C and was found to rearrange to m-cresol at −65 °C. The geometries of the bridged spiropentanes of this work were optimized at the MP2(frozen core)/6-31G* level of theory, and group equivalent values were derived in order to calculate the heats of formation for these compounds using the calculated energies.

1-Methylcyclopropylcarbene, generated by photolysis of two isomeric hydrocarbon precursors, undergoes ring-expansion readily to give 1-methylcyclobutene. Experimentally, intramolecular carbon-hydrogen insertions are not observed. Trapping studies with TME demonstrates the formation of the expected cyclopropane adduct, and via a double-reciprocal analysis, the lifetime of 1-methylcyclopropylcarbene was determined to be 12 ns in 1,1,2-trichlorotrifluoroethane. Computational studies show that the barrier to ring-expansion is significantly smaller in 1-methylcyclopropylcarbene than in cyclopropylcarbene. The origin of the increased rate of ringexpansion is due to stabilization of the positive charge that occurs at the incipient tertiary carbon that is attached to the migrating carbon center.

The triplet-triplet fluorescence and fluorescence excitation spectra of two new, planar diaryl carbenes in n-hexane and n-heptane were studied at cryogenic temperatures. Fluorescence decays were fitted to three exponential functions. Fluorescence decays of 12-oxo-5(12H)-naphthacenylidene were sensitive to the presence of a magnetic field, and this dependence allowed the estimation of the zero field splitting parameters (D) of the excited triplet state of this compound, which were 0.037 ( 0.010 and 0.03 ( 0.015 cm -1 for the low-and high-energy sites, respectively. These results are corroborated by computational studies of the ground-state preferences and the triplet excitation energies.