ChemInform Abstract: Thermochemistry of Organosilicon Compounds. Part 6. Thermochemical Properties of Organosilicon Compounds with a Si‐N Bond

Abstract

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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

“… 17 − 19 These are of lesser significance than first-hand (calorimetric) measurements, for which reason we have explicitly pointed out their use in the following discussion. The same is also true for the data reported by Voronkov et al 20 − 25 that have consistently been flagged dubious by Becerra and Walsh through comparisons with other reference data or with estimates based on reasonable chemical expectations. 17 − 19 …”

“…Third, after carefully evaluating the reliability of our thermochemical data, we use the W1X-1 results to derive group additivity contributions for the standard gas-phase enthalpy of formation, Δ f H 298K ° , entropy, S 298K ° , and heat capacity, C p , for 60 Benson groups and group pairs involving silicon. We show that the group contributions form internally consistent sets and compare them to those reported by Walsh and Becerra 18 and Janbazi et al 29 , 30 We also use our group contributions to determine the standard enthalpies of formation for several organosilicon species examined by Voronkov et al 20 − 25 that could not be calculated directly with the W1X-1 method simply due to molecular size. This allows a thorough assessment of the experimental data published by Voronkov et al for possible systematic errors.…”

“…As repeatedly discussed by Walsh and Becerra in their excellent reviews on the thermochemistry of organosilicon compounds, − the science of calorimetry has become almost extinct, and only a very few experimental values have been published for silicon-based species during the past 25 years. Furthermore, even the ones that have been published, such as the very comprehensive works of Voronkov et al, − have been questioned to be affected by systematic error(s) due to their incompatibility with other literature values that are often associated with high uncertainties themselves.…”

“…The calculated values are compared with experimental data, where available, allowing us to assess their accuracy and to pinpoint outliers and other inconsistencies. Of special interest are the results published by Voronkov et al, − in which case our aim is to determine whether the practice of flagging their data in thermochemical reviews is entirely justified. Second, we compare our results to the earlier CCSD­(T)/CBS benchmark values of Feller and Dixon, as well as to the recent computational works of Burcat and Goos and Janbazi et al , The data reported by Janbazi et al are found to be partially inconsistent with the other results, which is not only problematic by itself but also because the G4 enthalpies have been used as reference data in establishing group additivity contributions.…”

Addition/Correction to “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”

“… a See refs ( 9 − 14 ) for details of the experimental work. b Literature values (kJ mol –1 ): C–(C)(H) 3 = C–(H) 3 (O) = C–(H) 3 (Si) = −42.26, C–(C) 4 = 19.2, C–(C) 3 (H) = −1.17, C–(C) 2 (H) 2 = −20.63, C B –(C B ) 2 (H) = −13.81, C–(C)(H) 2 (O) = −32.90, C–(C)(H) 2 (S) = −23.17, S–(C) 2 = 46.99, tertiary corr = −2.26.…”