Abstract
N-(1-Methyl-1-phenylethyl)phenylacetamides exhibited strong growth-inhibiting activity against bulrush, Scirpus juncoides, and barnyard grass, Echinochloa crus-galli, in the vial tests. The phenylacetyl group was essential for the high activity against S. juncoides. Structure-activity relationships of N-(1-methyl-1-phenylethyl)phenylacetamides having various benzene ring substituents in the acid and amine moieties were analyzed with substituent parameters and regression techniques. The variation in the activity of 83 compounds was related parabolically with the hydrophobicity of the substituents. The steric factor was also important for the activity: it increased with a decrease in length of the 4-substituents in the acid moiety. Electron-withdrawing effect of the substituents at the 3- or 4-position in the amine moiety increased the activity, too. A similar equation was obtained against E. crus-galli. The growth-inhibiting activity was highly correlated with the herbicidal activity in the pot tests.
