Theoretical studies on new potential high energy density compounds (HEDCs) adamantyl nitrates from gas to solid

A series of adamantyl nitrates have been theoretically studied from gas to solid to search for new potential high energy density compounds (HEDCs). The heats of formation (HOFs) for the 26 title compounds were calculated by designing isodesmic reactions at the B3LYP/6-31G* level. It was found that the HOFs of the 26 isomers with the same number of -ONO₂ groups (n) are not correlated well with the corresponding substituted positions. According to the obtained heats of detonation (Q), detonation velocities (D), and detonation pressures (P) using the Kamlet-Jacobs equations, it was found that when n=7∼8, the adamantyl nitrates meet the criterion as an HEDC. The calculations on bond dissociation energies of O-N (E _O-N) showed that the adamantyl nitrates with gemi- ONO₂ always have the worst stability among the isomers, and all the adamantyl nitrates with gemi- ONO₂ have similar stability. Due to the complexity of their structures, values of E _O-N do not decrease with the increase of the substituent number n obviously, and the stability of adamantyl nitrates is not determined by only one structural parameter. Considering the stability requirement, only 1,2,4,6,8,9,10-adamantyl heptanitrate is recommended as a feasible HEDC. Molecular packing searching for 1,2,4,6,8,9,10-adamantyl heptanitrate among 7 most possible space groups (P2₁/c, P-1, P2₁2₁2₁, P2₁, Pbca, C2/c, and Pna2₁) using Compass and Dreiding force fields showed that this compound tends to crystallize in P2₁/c. Ab initio periodic calculations on the electronic structure of the predicted packing showed that the O-NO₂ bond is the trigger bond during thermolysis, which agrees with the result derived from the study of dissociation energies of O-N bonds. Supported by the National Natural Science Foundation of China (Grant Nos. 10576016 and 10576030) and the National 973 Project