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Comparison of CBS-QB3, CBS-APNO, and G3 Predictions of Gas Phase Deprotonation Data

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journal contribution
posted on 23.10.2001, 00:00 by Emma K. Pokon, Matthew D. Liptak, Steven Feldgus, George C. Shields
The G3, CBS-QB3, and CBS-APNO methods have been used to calculate ΔH and ΔG values for deprotonation of seventeen gas-phase reactions where the experimental values are reported to be accurate within one kcal/mol. For these reactions, the mean absolute deviation of these three methods from experiment is 0.84 to 1.26 kcal/mol, and the root-mean-square deviation for ΔG and ΔH is 1.43 and 1.49 kcal/mol for the CBS-QB3 method, 1.06 and 1.14 kcal/mol for the CBS-APNO method, and 1.16 and 1.28 for the G3 method. The high accuracy of these methods makes them reliable for calculating gas-phase deprotonation reactions, and allows them to serve as a valuable check on the accuracy of experimental data reported in the National Institutes of Standards and Technology database.