Alkaline hydrolysis of diethyl N-acetylamino(3,5-di-tert-butyl-4-hydroxybenzyl)malonate is accompanied by decarboxylation. The efficiency of this process depends on the temperature and ratio of the reactants. A possibility of tautomerism with migration of the proton of phenolic hydroxyl and the influence of the structure on the antioxidation properties were considered on the basis of analysis of the IR spectral data and quantum chemical (PM6) calculation of the structures. The energies of homolysis of the OH bond of phenolic hydroxyl were calculated for a series of the synthesized compounds. It is proposed to predict the antioxidation activity on the basis of these values.