The main theoretical methods for the calculation of the thermochemical char
acteristics of organic compounds are analyzed: the additive group method, t
he method of comparative calculation and semiempirical and ab initio quantu
m chemical calculations. The application of these procedures to the estimat
ion of enthalpies of the formation of polyoxides ROnR' is discussed (n = 2,
3, 4; R and R' are organic substituents or a hydrogen atom).