ABSTRACT:In earlier studies (Gross and Seybold, Int J Quantum Chem, 2001, 85, 569; Gross et al., Int J Quantum Chem, 2002, 90, 445), it was shown that variations in several calculated quantum chemical charge and energy parameters were strongly correlated with the pK a variations in a set of substituted phenols. Here, we examine whether this approach can be extended to the pK a s of a diverse set of more complex organic phenolic compounds. Three levels of theory were tested: (1) the RM1 semiempirical method, with and without the SM5.4 solvent model, (2) density functional theory at the B3LYP/6-311G** level, and (3) single-point B3LYP/6-31ϩG* calculations with the self-consistent reaction field SM8 solvent model. The best results were obtained with quantum chemical indices calculated using the SM8 solvent model.

Most acidities and basicities of chemical compounds are measured in aqueous solution since this solvent is most important for biochemical and environmental applications, but the acidities of compounds in the gas phase and in other solvents can also be of interest. As a polar, aprotic solvent, dimethyl sulfoxide (DMSO) presents a unique environment for acid dissociation, and this solvent offers informative comparisons with both the vacuum and aqueous environments. Here, quantum chemical approaches previously used for the estimation of aqueous pKa values are applied to the estimation of DMSO, aqueous, and gas‐phase acidities for two representative series of compounds: alcohols/phenols and azoles. Calculations were performed using both the semiempirical RM1 method and density functional theory (B3LYP/6‐31+G**). The effectiveness of the SM5.4 and SM8 solvent models in estimating the solution‐phase acidities was also examined. © 2012 Wiley Periodicals, Inc.

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