MOLECULAR-PROPERTIES AS DESCRIPTORS OF OCTANOL-WATER PARTITION-COEFFICIENTS OF HERBICIDES

Molecular modeling techniques were used to establish relationships bet ween the octanol/water partition coefficient (K-ow) and molecular prop erties of 90 herbicides with several types of chemistry. The K-ow valu es were obtained from the literature. Various molecular properties wer e calculated by quantum mechanical methods using molecular modeling so ftware. The quantitative structure activity relationship (QSAR) analys is of all herbicides showed that K-ow was dependent on bulk (van der W aals volume, VDWV) and electronic (dipole moment, mu; superdelocalizab ility of highest occupied molecular orbital, S-HOMO; nucleophilic supe rdelocalizability, 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 dinit roanilines) based on structural similarities, and separate equations w ere established for each group. The QSAR models accounted for 74 to 98 % of the variation in K-ow within these six groups. Applicability of t hese models was tested for some herbicides. The QSAR models produced e stimates that correlate well with experimental values and appear to be specific to structurally similar compounds.