The energetic study of 2-methylnaphtho[1,2-d] oxazole (MN12O), 2-methylnaphtho-[2,3-d] oxazole (MN23O) and 2-methylnaphtho[1,2-d] thiazole (MN12T) has been performed experimental and computationally. The enthalpies of combustion and sublimation/vaporization of these compounds were determined, respectively, from static or rotating bomb combustion calorimetry and high temperature Calvet microcalorimetry and/or the Knudsen-effusion studies. These experimental data allow derivation of the corresponding gas-phase standard molar enthalpies of formation of the three compounds. Additionally, we have obtained the gas-phase standard molar enthalpies of formation of these three compounds, as well of the 2-methylnaphtho[2,3-d] thiazole (MN23T), through high level ab initio calculations, at the G3(MP2)//B3LYP and DLPNO-CCSD(T)/cc-pVTZ levels of theory. The computational study of the molecular structures of the compounds has been carried out. Furthermore, a relationship between the energetic and structural characteristics of these molecules was also evaluated. (C) 2018 Elsevier Ltd.