Anthrone, coumarin and phenazine were studied by combustion calorimetry of small amounts of substance, sublimation calorimetry, neat capacity measurements and differential thermal analysis.The thermodynamic quantities derived at 298.15 K allowed us to determine some energy valuez related to molecular structure which enabled us to realize a comparative study for the two isomers: chromone and coumarin, and determine an enthalpy value for some intramolecular chemical bonds in the molecules studied.