HERBICIDAL SELECTIVITY OF (E)-3-(2,4-DICHLOROPHENOXY)ACRYLATES - QSARSTUDY WITH MOLECULAR CONNECTIVITY INDEXES

The aim of this study was to generate a quantitative model of the herb icidal selectivity of (E)-3-(2,4-dichlorophenoxy)acrylates against bar nyard grass and rice. Molecular connectivity indices and other topolog ical quantities were used as molecular descriptors. A solid and sound correlation (r = 0.91) was obtained between the selectivity index DELT ApI50 (defined as logarithmic ratio of biological activities observed in the two tested plant species) and the three topological quantities: the first-order molecular connectivity index, the valence fifth-order path/cluster molecular connectivity index, and the presence of a cycl ic alcohol moiety. Our QSAR analysis revealed that the size of a molec ule accounts for a large part of the variation in the DELTApI50 data. However, the degree of branching and the presence of a cyclic group in the alcohol moiety have a significant influence on the selectivity of (E)-3-(2,4-dichlorophenoxy)acrylates. The derived selectivity model, when compared with the corresponding empirical model, based on the I-o ctanol/water partition coefficient and Taft's polar constant, shows a far superior performance in accuracy.