A THEORETICAL STUDY OF ALTERNATIVE PRIMARY REACTIONS MECHANISMS OF GAS-PHASE THERMAL DECOMPOSITION OF THE N-METHYL-N´-METHOXYDIAZENE-N-OXIDE. PART 2. N-METHYL-N´-METHOXYDIAZENE-N-OXIDE STRUCTURE AND ROTATION REACTIONS OF ITS FUNCTIONAL GROUPS AND MET

Using the density functional methods PBE, B3LYP, wB97XD, wB97X with different sets of basis functions, as well as the composite G4 method, the rotation reactions of methyl groups at nitrogen and oxygen atoms in two Z-conformers, differing in the rotation of the CH3O group relative to the plane of the molecule, and the Е-conformer of the simplest representative of an alkoxy-NNO-azoxy compound - N-methyl-N’-methoxydiazene-N-oxide were studied. It has been confirmed that in the structures corresponding to the minima on the potential energy surface, the hydrogen atoms of the CH3 groups have a “checkerboard” arrangement, which is consistent with the available experimental data. It has been proven that for the most energetically favorable Z-conformation of N-methyl-N’-methoxydiazene-N-oxide, where the fragment of the molecule C-(O)N=N-O-C is planar, and the oxygen atoms at the double bond N=N are in the cis-position, there is only one structure corresponding to the minimum energy - with the rotation angle of the methyl group at the nitrogen atom (H7C1N2N3) equal to 0o. It is shown that in the transition states of rotation of methyl groups in all three conformers of N-methyl-N’-methoxydiazene-N-oxide, hydrogen atoms form “eclipsed” structures. The activation barriers of the reactions under discussion were estimated. It was found that in the Z-conformer the rotation of the CH3 groups located both at the nitrogen atom and at the oxygen atom is free. The values of activation enthalpies calculated for these reactions are within the experimental error - 3-4 kJ/mol. For the E- and Z’- conformers of N-methyl-N’-methoxydiazene-N-oxide, the rotation barriers of both methyl groups are somewhat higher (they are within 19-25 kJ/mol according to data from different methods), but these reactions also proceed practically freely. With increasing temperature, a decrease in the activation enthalpy of the reactions under discussion is observed. It is noted that the data from all methods used in the work are in good agreement with each other. The article is dedicated to the memory of Shamov Alexander Georgievich.