The energies of combustion and fusion of 5-cyano-5H-dibenzo [a,d]cycloheptene (1) and (5E,11E)-dibenzo[a,e]cyclooctene-5,11-dicarbonitrile (2) were measured by means of microbomb calorimetry and DSC, respectively. The derived enthalpies of formation in solid state are 320 ± 18 for nitrile 1 and 470 ± 31 kJ mol -1 for nitrile 2, respectively. The experimental enthalpies of formation are discussed in relationship with values calculated at the G3(MP2)//B3LYP level of quantum chemical theory, by means of group additivity and isodesmic reactions. The two nitriles are not stabilized by dibenzoannelation.Keywords Dibenzocycloalkane nitrile Á Enthalpies of combustion and of formation Á Enthalpies of fusion, vaporization and sublimation Á G3(MP2)//B3LYP quantum chemical calculations Á Group additivity Á Isodesmic reactions