cf. CA 57, 5107i.An explanation based on the concept of lowest localization energy (K region) in a C-C bond is suggested to explain the comparative rates of biol. oxidation of naphthalene, anthracene, phenanthrene, and their substituted products, in the presence of soil pseudomonads.Substitution at angular carbons blocks the oxidation to salicylic acid or its analogs, the normal ultimate products of end ring fission.It is proposed that the change in site of oxidation on degradation by an enzyme of an aromatic compound may be due to activation in the enzyme-substrate complex of a bond of normal secondary reactivity in the substrate mol.