Estimation of Aqueous-Phase Reaction Rate Constants of Hydroxyl Radical with Phenols, Alkanes and Alcohols

A quantitative structure activity relationship (QSAR) model was developed for the aqueous-phase hydroxyl radical reaction rate constants (k(OH)) employing quantum chemical descriptors and multiple linear regressions (NILR). The QSAR development followed the OECD guidelines, with special attention to validation, applicability domain (AD) and mechanistic interpretation. The established model yielded satisfactory performance: the correlation coefficient square (R-2) was 0.905, the root mean squared error (RMSE) was 0.139, the leave-many-out cross-validated Q(LMO)(2) was 0.806, and the external validated Q(EXT)(2) was 0.922 log units. The AD of the model covering compounds of phenols, alkanes and alcohols, was analyzed by Williams plot. The main molecular structural factors governing k(OH) are the energy of the highest occupied molecular orbital (E-HOMO), average net atomic charges on hydrogen atoms (Q(H)) over bar molecular surface area (MSA) and dipole moment (mu). It was concluded that k(OH) increased with increasing E-HOMO and MSA, while decreased with increasing (Q(H)) over bar and mu.