Structure-activity relationship in the auxin activity of mono-substituted phenylacetic acids

The analysis of substituent constants for the lipophilic and electronic factors in the auxin activity of substituted phenylacetic acids in elongation of coleoptile segments shows that these factors parallel those for the phenoxyacetic acids but assign reactivity in growth promotion to the meta position of phenylacetic acid. The inhibitory effects with supra-optimal concentrations are highly dependent on the lipophilic character of the molecules.