A THEORETICAL STUDY OF ALTERNATIVE PRIMARY REACTIONS MECHANISMS OF GAS-PHASE THERMAL DECOMPOSITION OF THE N-METHYL-N´-METHOXYDIAZENE-N-OXIDE. PART 1. N-METHYL-N´-METHOXYDIAZENE-N-OXIDE STRUCTURE AND REACTIONS OF ITS CONFORMATIONAL TRANSITIONS
Rubrics: 1. CHEMISTRY
Authors:
1.
KNITU
2.
KNITU
3.
Kazanskiy filial Mezhvedomstvennogo Superkomp'yuternogo Centra RAN; Kazan' branch of the interdepartmental super-computer centerRAS
4.
KNITU
5.
KNITU; Kazan National Research Technological University
Type:
Article
Pages:
from 9
to 17
Status:
In work
Language:
Russian
Keywords:
QUANTUM CHEMICAL CALCULATION, N-METHYL-N’-METHOXYDIAZENE-N-OXIDE, STRUCTURE, Z- AND E-CONFORMERS, TRANSITION STATES, ROTATION OF FUNCTIONAL GROUPS
Abstract (English):
Four isomeric structures of the simplest representative alkoxy-NNO-azoxy compound - N-methyl-N’-methoxydiazene- N-oxide were studied using PBE, B3LYP, wB97XD, wB97X density functional methods with different sets of basis functions. It was confirmed that the most energetically advantageous configuration of this compound is the Z-conformation, where the fragment of the molecule C-(O)N=N-O-C is flat, and the oxygen atoms at the N=N double bond are in the cis-position. 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 in the trans-position, is less stable. This conclusion also applies to structures corresponding to two rotational mirror isomers of the Z-conformation formed as a result of 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 isomers of N-methyl-N’-methoxydiazene-N-oxide were studied. Transition states were found and reaction barriers were calculated at two temperatures - normal conditions and the average temperature of the existing experimental study. In addition to the above density functional methods, the composite method G4 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 gas-phase thermal decomposition of N-methyl-N’-methoxydiazene-N-oxide made it possible to conclude 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 Alexander Georgievich.
Four isomeric structures of the simplest representative alkoxy-NNO-azoxy compound - N-methyl-N’-methoxydiazene- N-oxide were studied using PBE, B3LYP, wB97XD, wB97X density functional methods with different sets of basis functions. It was confirmed that the most energetically advantageous configuration of this compound is the Z-conformation, where the fragment of the molecule C-(O)N=N-O-C is flat, and the oxygen atoms at the N=N double bond are in the cis-position. 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 in the trans-position, is less stable. This conclusion also applies to structures corresponding to two rotational mirror isomers of the Z-conformation formed as a result of 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 isomers of N-methyl-N’-methoxydiazene-N-oxide were studied. Transition states were found and reaction barriers were calculated at two temperatures - normal conditions and the average temperature of the existing experimental study. In addition to the above density functional methods, the composite method G4 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 gas-phase thermal decomposition of N-methyl-N’-methoxydiazene-N-oxide made it possible to conclude 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 Alexander Georgievich.
Keywords:
QUANTUM CHEMICAL CALCULATION, N-METHYL-N’-METHOXYDIAZENE-N-OXIDE, STRUCTURE, Z- AND E-CONFORMERS, TRANSITION STATES, ROTATION OF FUNCTIONAL GROUPS
QUANTUM CHEMICAL CALCULATION, N-METHYL-N’-METHOXYDIAZENE-N-OXIDE, STRUCTURE, Z- AND E-CONFORMERS, TRANSITION STATES, ROTATION OF FUNCTIONAL GROUPS
