Standard ab initio packages such as Gaussian are used for optimizing ground state and transition state geometries. Frequency calculations are carried out as well for unambiguous characterization of the stationary points. These results are then used to estimate TST and RRKM rate constants for comparison with our experimental results. Hartree-Fock level calculations are grossly inadequate for HX elimination reactions. Among the methods that include electron correlation, we find that DFT calculations give much better results for the activation energy of HX elimination reactions compared to MP2 methods at much lower computational cost. Recently, we have looked at HX elimination reactions from HNXY, CH3CH2X and CH2X-CH2X (X = F/Cl). Higher level calculations based on G2 methods have been used for calculating enthalpies of formation of all the reactants, products and intermediates accurately. Currently, we are looking at haloethanols CH2X-CH2OH which have the possibility of HX and H2O elimination.