The article discusses the evaluation of the aromatic compounds pathways transformations – widespread xenobiotics of aqueous systems. This issue has both theoretical (chemical lability in complex reaction systems) and applied (target designation for the development analytical methods) meaning. Benzoic, 4-hydroxybenzoic, 2-hydroxybenzoic, 2-chlorobenzoic acids, 4-hyd-roxybenzoic acid methyl ester, and salicylic ester of acetic acid were chosen as objects of investigation. They have been used in

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... od, pharmaceutical, cosmetic industries as preservatives, in chemical industry and laboratory practice as starting materials for the synthesis of new organic compounds, in analytical chemistry as reagents, chromophores, and standards in calorimetric analysis. We used quantum chemical modeling mechanisms of abiotic and biodegradation of functionalized arenes as a research method. It has been shown that for the transformation of benzoic acid, including oxidative breaking of cycle, the most probable is the path through 2,3-di-hydroxybenzoic acid to 1,3-butadiene-1,1,4-tricarboxylic acid (the product of the intradiol oxidative breaking of the cycle). There is transformation path through 2,3-dihydroxybenzoic acid to 1,3-butadiene-1,1,4-tricarboxylic acid (product intradiol oxidative rupture of the cycle) realized for 2-hydroxybenzoic acid (compound itself and the products of the conversion of salicylic ester of acetic acid, 2-chlorobenzoic acid). Pathway is observed through 3,4-dihydroxybenzoic acid to 1,3-butadiene-1,2,4-tricarboxylic acid (the product of the intradiol oxidative break cycle) for 4-hydroxybenzoic acid (compound itself and the product of the conversion of 4-hydroxybenzoic acid methyl ester). As it follows from the above, the intraradiol path of the oxidative cycle breaking seems to be the most preferable. Accordingly, a preferential accumulation of the following substances should be expected as results of the samples transformation: 2- and 4-hydroxybenzoic acids, 2,3- and 3,4-dihydroxybenzoic acids, products of the radical oxidative breaking of the cycle and the results of their further transformation.