Özet:
The unimolecular, ground-state, four-center hydrogen fluoride elimination from vinyl fluoride, 1,1-difluoroethylene, trans-1,2-difluoroethylene, and trifluoroethylene reactions were investigated in this thesis. Hartree-Fock and Density Functional Theoretical calculations were performed to identify the stationary points in terms of their geometrical parameters and energies on the potential energy surface for each reaction under consideration. The entire study is composed of two parts: In the first part, the equilibrium geometries, infrared vibrational frequencies, and the energies of the reactants, four-center transition states, and the products were obtained at the Hartree-Fock Theory and Density Functional Theory by using Becke-style three-parameter functional. Five types of basis sets, composing of 6-31G*, 6-31G**, 6-31+G*, 6-311G*, and 6-311+G**, were used together with each method in the calculations, in order to search the possible effects of the basis sets on the results. In the second part, an alternative Density Functional Theory approach was used. All the geometries of the involved species were obtained at LDA/DZ, LDA/TZP, and LDA/TZ2P levels. Intrinsic Reaction Coordinate (IRC) analyses, in terms of geometry, energy, and gross atomic charge changes during the course of the reactions were applied at LDA/TZ2P level in order to follow the mechanism of eliminations. In all cases the obtained results were compared with the available corresponding theoretical and, if possible, experimantal literature values. Generally, the results were found to be quite reasonable and in alignment with literature.
