Thermodynamic Characterization of Condensed-Ring Compounds. Annual Technical Summary Report, December 1, 1984-December 31, 1985

摘要

Development of fundamental thermodynamic relationships on organic materials from fossil substances proceeded along several fronts that ranged from proof studies for ab initio quantum mechanical calculations to application of basic thermodynamic relationships to determine the influence of molecular shape and hydrogen bonding on the thermophysical properties of fluids. Recently obtained experimental data were used to extend and refine ''Benson'' group contributions for the prediction of gas phase enthalpies of formation and entropies. The results were used to show that presently used formulations do not predict the temperature dependence of these properties adequately. Investigations were also made with molecular mechanics calculations for the correlation and prediction of thermodynamic data. These procedures combine empirical group contributions with force fields to account for nonbonded interactions and with quantum mechanical calculations to account for the stabilizing influence of extended pi-electron systems. The results show more predictive promise than the Benson method for estimation of enthalpies of formation at 298.15 K. The need for refinement of group contributions from this method was shown with test calculations using new data obtained at NIPER in related projects. The refinements are planned for the coming year. These procedures were also used to predict potential functions for large amplitude vibrations in high molecular weight compounds. Large amplitude vibrations make large contributions to the thermodynamic properties, and they are difficult to determine from spectroscopic data. Experimental tests are in progress to determine if such vibrations can be predicted with sufficient accuracy for 9,10-dihydroanthracene which has a large amplitude vibration and which has been used as a model substance in many hydrogen transfer studies. 37 refs., 6 figs., 4 tabs. (ERA citation 11:041182)