Prediction of the standard enthalpy of formation (ΔfH0298) of boron nitride nanocone (BNNCs) structureswith disclination angles 60°, 120°, and 180°is recommended to be performed by the isodesmic reaction approach. NH3 ,BH3 , and N2 H4 were selected as key reference compounds. In order to calculate ΔfH0298 of nanocones, we must firstcalculate the enthalpies of nanocone rings at their apexes. For this purpose, ΔfH0298 values of 40 different structures, suchas boron, nitrogen, and hydrogen compounds, have been calculated by combining Gaussian-4 (G4) theory calculationswith the isodesmic and other balanced reactions approach. At each stage of the calculations, the previously estimatedenthalpies of formation of nanocones were used as reference points for new molecules in the isodesmic and other balancedreactions. The results of enthalpies of formation of reference compounds were then used as reference values to estimatethe enthalpy of formation of rings of BNNCs at their apexes. Finally, enthalpies of formation of BNNCs with disclinationangles of 60°, 120°, and 180°and cone heights of 1–5 Å, 3–7 Å, and 4–8 Å were calculated. The results show that thereactions are highly exothermic. An increase in cone height causes the enthalpy of formation of boron nitride nanoconestructures to become more negative.