An additivity scheme for the estimation of heats of formations,entropies, and heat capacities of silanes,polysilanes, and their alkyl derivatives

Heat of formation data available for silanes and alkylsilanes have been evaluated using the Benson-Luria electrostatic energy corrected bond additivity method for a priori calculations of heats of formation of hydrocarbons. It is concluded that the calculational method is applicable to silanes and alkylsilanes, and that the recent combustion measurements employing HF and O₂ are reliable. Group additivity enthalpies based on these data are presented. Results of a large number of statistical thermodynamic calculations of entropies and heat capacities are also given, and values of the group additivities derivable from these results are presented. Internal consistencies of estimated thermodynamic properties (i.e., estimated reaction enthalpy, entropy, and heat capacity changes) are thought to be reliable to within ±1.5 kcal and ±1.0 e.u., respectively. Group additivity estimates for individual compounds could be significantly less accurate due to the limited accuracy and extent of the ΔH⁰_f data base, and to the uncertainties in assigned frequencies and internal rotational barriers employed in calculating entropies and heat capacities.