A group additivity methodology for predicting the thermochemistry of oxygen‐containing organosilanes

Abstract

A combinatorial approach was applied to devise a set of reference Si-CO -H species that is used to derive group-additivity values (GAVs) for this class of molecules. The reference species include 62 stable single-bonded, 19 cyclic, and nine double-bonded Si-CO -H species. The thermochemistry of these reference species, that is, the standard enthalpy of formation, entropy, and heat capacities covering the temperature range from 298 to 2000 K was obtained from quantum chemical calculations using several composite methods, including G4, G4MP2, and CBSQB3, and the isodesmic reaction approach. To calculate the GAVs from the ab initio based thermochemistry of the compounds in the training set, a multivariable linear regression analysis is performed. The sensitivity of GAVs to the different composite methods is discussed, and thermodynamics properties calculated via group additivity are compared with available ab initio calculated values from the literature.

High-Level Ab Initio Predictions of Thermochemical Properties of Organosilicon Species: Critical Evaluation of Experimental Data and a Reliable Benchmark Database for Extending Group Additivity Approaches

“…Even more perplexing is the observation that the G4 data reported by Janbazi et al 30 for silanols and alkoxysilanes in their second paper are in much better agreement with our values in Table 1 than what was seen in the case of simple (alkyl)silanes. This is surprising, given that the same composite method and atomization approach were used in both studies.…”

“…As discussed earlier, the inaccuracies in the computed enthalpies reported by Janbazi et al 29 , 30 raise concerns over the group contribution values they have determined. In fact, the group contributions given by Janbazi et al do not reproduce all G4-level enthalpies from which they are derived.…”

Thermochemistry of Oxygen-Containing Organosilane Radicals and Uncertainty Estimations of Organosilane Group-Additivity Values

“…However, limitations remain. In a previous study, Janbazi et al 18 tried to derive GAVs of cyclosiloxanes. This attempt did not turn out to be of practical relevance because cyclosiloxanes with 6, 8, and 10 atoms in the ring (Si 3 O 3 , Si 4 O 4 , and Si 5 O 5 ) were shown to have different GAVs for analogue group increments.…”

“…• SiH 2 CH 3 , and • CH 2 SiH 3 , uncertainty contributions of group increments appearing in these species, such as Si−(H) 3 (Si) and C−(H) 3 (Si), were derived by also applying the root sum squared method. In addition, uncertainty contributions of 18,19 in a stepwise way.…”

“…In another recent publication from our group on the thermochemistry of stable Si−C−H−O molecules, we assumed an overall uncertainty regarding computed reaction enthalpies of ±12.6 kJ/mol to adhere to the 95% confidence interval. 18 Now, in order to derive consistent uncertainty estimates of GAVs, we revised all reported uncertainties of stable Si−C−H species and Si−C−H radicals by using an isodesmic-reaction-enthalpy uncertainty contribution of ±12.6 kJ/mol. This correction leads to an increase in uncertainty by approximately 2 kJ/mol for each ΔH f °; that is, all uncertainty estimates for Si−C−H reported in ref 19 increase by approximately 2 kJ/mol.…”