Alternative mechanisms of the primary act of gas-phase monomolecular thermal decomposition of N-methyl-N’-methoxydiazene-N-oxide according to the data of quantum chemical calculations

Abstract

The mechanisms of the primary act of thermal decomposition of the simplest representative of the series of alkoxy-NNO-azoxy compounds – N-methyl-N’-methoxydiazene-N- oxide are studied using quantum-chemical density functional methods PBE, B3LYP, wB97XD with different sets of basic functions, as well as the composite G4 method. It is shown that the most probable channel of its thermal destruction, leading to the formation of experimentally observed reaction products, is isomerization because of rotation of the OCH3 group around the NO bond with the subsequent transfer of the CH3 group between oxygen atoms. In this case, the transfer of the CH3 group is the limiting reaction of the thermal decomposition of N-methyl-N’-methoxydiazene-N-oxide as a whole.

Quantum chemical investigation of the 1‐methyl‐ and 1‐neopentyl‐2‐methoxydiazene‐1‐oxides thermal decomposition mechanisms

“…It can be seen from Table 2 that the DFT calculation data for TS3 are slightly underestimated compared to CCSD and, at the same time, correspond to the results of the DFT calculations in Nikolaeva et al [20] As well as in Xiong et al, [24] for the PBE0/cc-pVDZ results, the reverse order of the O-CH 3 and N-OCH 3 bond energies is obtained (see above). For R1 + CH 3 Ȯ and R2 + _ CH 3 , the results obtained by the PBE0 and CCSD methods are fairly similar.…”

“…Based on experimental data on the kinetics of gas‐phase decomposition of compound 1 , [ 18 ] the authors of Nikolaeva et al, [ 20 ] using DFT and G4 quantum‐chemical calculations, proposed an alternative mechanism of this reaction, including the migration of the methyl group from the O 2 atom to the O 1 atom at the limiting stage. In essence, this is an intramolecular nucleophilic substitution reaction (S N 2) in which the nucleophile is the O 1 atom.…”

“…[ 18 ] More recently, based on density‐functional theory (DFT) and G4 quantum‐chemical calculations, an alternative mechanism of decomposition of compounds 1 has been proposed, [ 20 ] which consists in the rotation of the OCH 3 group around the N‐O bond followed by the transition of the CH 3 group to another oxygen atom (the limiting reaction stage of thermal decomposition via this channel). The activation enthalpy of such transformation is 184 kJ/mol, [ 20 ] which corresponds well to the experiment. [ 18 ] N , O ‐dimethyl‐ N ‐nitrosohydroxylamine ( 3 ) formed by such a transfer of the CH 3 group is a well‐known compound.…”

“…[18] For the decomposition of compounds 1 and 2, a fairly reasonable mechanism of homolytic breaking of the weakest bond N-OCH 3 was proposed. [18] More recently, based on density-functional theory (DFT) and G4 quantum-chemical calculations, an alternative mechanism of decomposition of compounds 1 has been proposed, [20] which consists in the rotation of the OCH 3 group around the N-O bond followed by the transition of the CH 3 group to another oxygen atom (the limiting reaction stage of thermal decomposition via this channel). The activation enthalpy of such transformation is 184 kJ/ mol, [20] which corresponds well to the experiment.…”