CONFORMATIONAL-ANALYSIS .129. HEATS OF FORMATION AND THERMODYNAMIC PARAMETERS FOR HYDROCARBONS, CALCULATED BY THE MOLECULAR MECHANICS METHOD INCLUDING THE EFFECTS OF MOLECULAR VIBRATIONS

Title full: Conformational analysis-129. Heats of formation and thermodynamic parameters for hydrocarbons, calculated by the molecular mechanics method including the effects of molecular vibrations1 1 Paper 128, T. Liljefors and N.L. Allinger, J. Am. Chem. Soc. 100, 1068 (1978).,2 2 Supported by Grant CHE74-08071 from the National Science Foundation. Abstracted from the Ph.D. dissertation of D.H.W., submitted to the University of Georgia (1974). A force field is presented in which the zero point energies and the effects of vibrational thermal excitation are included in the heat of formation calculations. The standard deviation of the difference between the calculated and experimental heats of formation of a diverse set of 44 hydrocarbons is 0.38 kcal mole, which is the same as the average experimental error for this set of compounds. This standard deviation is substantially lower than in previous similar force fields which did not include vibrational effects, and it is argued that much of this improvement is due to the inclusion of vibrational terms in the heat of formation. This force field also reproduces the experimental structures of compounds well. © 1979.