The question of determining the thermodynamic characteristics of a substance is a fundamental problem of modern physical chemistry. Thus, their analysis allows one to study reactions both from the point of view of mechanisms and from a quantitative point of view - the calculation of equilibrium constants, rates, bond dissociation energies, enthalpies of substances and processes, etc. The development of computer technology and the development of new quantum chemical methods make it possible to carry out theoretical calculations of the thermodynamic properties of chemical compounds with an accuracy comparable to the errors of experimental studies.