Molecular properties as descriptors of octanol-water partition coefficients of herbicides

Molecular modeling techniques were used to establish relationships between the octanol/water partition coefficient (K-ow) and molecular properties of 90 herbicides with several types of chemistry. The K-ow values were obtained from the literature. Various molecular properties were calculated by quantum mechanical methods using molecular modeling software. The quantitative structure activity relationship (QSAR) analysis of all herbicides showed that K-ow was dependent on bulk (van der Waals volume, VDWV) and electronic (dipole moment, mu; superdelocalizability of highest occupied molecular orbital, S-HOMO; nucleophilic superdelocalizability, S-N) properties, and the model explained 68% of the variation in K-ow. Herbicides were broadly divided into six families (ureas, acid amides, triazines, carbamates, diphenyl ethers, and dinitroanilines) based on structural similarities, and separate equations were established for each group. The QSAR models accounted for 74 to 98% of the variation in K-ow within these six groups. Applicability of these models was tested for some herbicides. The QSAR models produced estimates that correlate well with experimental values and appear to be specific to structurally similar compounds.