Computational investigations of reaction thermochemistry and mechanism

Several approximate and semiempirical molecular orbital methods are examined and applied to the computation of the structures, electronic properties, and relative energies of molecules, with an emphasis on examining the Cope and oxy-Cope reactions. It is demonstrated that the AM1/RHF method may be used to accurately calculate O-H bond dissociation energies. While none of the methods examined could be used for the direct calculation of electron affinities, it is shown that electron affinities of unknowns can be estimated by correlating the calculated charge on the atom which accepts the electron and experimental electron affinities of similar molecules. The use of kinetic and equilibrium isotope effects for testing the validity of calculated transition state structures is also examined. Finally, the Extended Huckel method has been modified and reparameterized to allow for the calculation of molecular geometries. The geometries of several nickel complexes have been calculated using this method, and a possible explanation for the observed differences in geometries of four-coordinate nickel complexes is examined.