These results represent the experimental contribution to the study of the thermodynamic properties of 3,5-di-tert-butyl-o- benzoquinone and 3,6-di-tert-butyl-o-benzoquinone. As we can see from table 5 for compared quinones, which are isomers, there is a tendency to an increase in the enthalpy of formation. It should be noted that the experimental values obtained for combustion energies, enthalpies of combustion and formation for tested in present work 3,5-di-tert-butyl-o-benzoquinone are in a good agreement with the values reported in Ref. [25] (see table 5). Moreover these results are consistent with the trend for the series of di-tert-butyl-substituted benzene [39].