Richard W. Counts

Geometry optimization within a modified extended HÜckel formalism : modifications to the ased program

Abstract The ASED program by Anderson and coworkers was modified to include a full geometry optimizer. It was discovered that, even with this modification, the ASED program could not be used to perform geometry optimizations on organic molecules without further modification. These modifications included changing the Wolfsberg-Helmholz equation used in the ASED program back to the original equation found in the FORTICON8 program as well as changing the Slater orbital exponents. A general parameter set for C, H, O and N has been developed, which has been used to perform geometry optimizations on selected organic molecules. The calculated geometries compared reasonably with the experimental values and with previously published AM1 geometries.

Semiempirical computation of homolytic O-H bond dissociation energies of alcohols: comparison of the AM1 and PM3 methods

Abstract The heats of formation of various alcohols and alkoxy radicals were calculated using the AM1 and PM3 semiempirical methods, which were then used to calculate the bond dissociation energies of the alcohols. Both restricted Hartree-Fock (RHF) and unrestricted Hartree-Fock (UHF) calculations were performed to determine which technique was most applicable to the computation of bond dissociation energies within the semiempirical frameworks. It was determined that AM1/RHF calculations gave the most accurate results for O-H bond dissociation energies of alcohols. The effect of using configuration interaction calculations to calculate bond dissociation energies within the semiempirical framework was also examined.

Empirical method for the estimation of electron affinities

Abstract AM1 calculations were made to obtain the Mulliken population analysis charges for selected oxy anions. It is shown that the charges may be correlated with the experimental electron affinities of the associated oxy radicals, and that the resulting correlation may then be used to predict the electron affinities of other oxy radicals. The above correlation suggests that the ability of an oxy radical to accept an electron is dependent on the ability of the oxy anion to delocalize the charge through either the σ or π framework of the molecule (via induction or resonance). Comparisons are also made between this work and recent work by others on the acidity of alcohols and carboxylic acids. Finally, it is demonstrated that the calculated electron affinities of selected oxy radicals can be used along with calculated O-H bond dissociation energies of the corresponding alcohols to determine gas phase acidities of certain alcohols, which in turn can be used to calculate the heats of formation of oxy anions.