Four isomeric structures of the simplest representative of alkoxy-NNO-azoxy compounds—N-methyl-N'-methoxydiazene-N-oxide—have been studied using PBE, B3LYP, wB97XD, and wB97X density functional theory methods with different basis sets. The results confirm that the most energetically advantageous configuration of this compound is the Z conformation, where the C–(O)N=N–O–C moiety of the molecule is flat, and the oxygen atoms at the N=N double bond are cis to each other. The configuration of the N-methyl-N'-methoxydiazene-N-oxide molecule corresponding to the E conformation, where the oxygen atoms at the N=N double bond are trans to each other, is less stable. This conclusion also applies to structures corresponding to two rotational mirror isomers of the Z conformation formed through the rotation of the CH3O group around the NO bond. The relative enthalpies of formation of the last three structures are about 17–18 kJ/mol higher than that of the Z conformer. Reactions of mutual transformation of N-methyl-N'-methoxydiazene-N-oxide isomers have been studied. Transition states have been found, and reaction barriers have been calculated at two temperatures, under normal conditions and at the average temperature of the existing experimental study. In addition to the above density functional theory methods, the composite G4 method was also used. All methods used in the work give consistent results. Comparison of the calculated reaction barriers of conformational transitions with the experimentally determined enthalpy of activation of the gas-phase thermal decomposition of N-methyl-N'-methoxydiazene-N-oxide enables the conclusion that the studied processes may compete with other alternative thermal degradation channels of this compound. However, the final answer in this matter can be given only after a detailed study of the secondary processes. The article is dedicated to the memory of Shamov Alexandr Georgievich.
Nikolaeva et al. (Sun,) studied this question.