Conformational analysis, tautomeric preference, intramolecular hydrogen bonding, and solvent effect on dinitrosamine: A quantum chemical study

摘要

HF, B3LYP, and MP2 methods with the standard basis set, 6-311++G(d,p), were used to study various aspects of dinitrosamine. These results were compared with the outcomes of G2 and CBS-QB3 methods. First, the conformational analysis and characterization of equilibrium conformations, especially global minima, were performed. On the basis of relative energies, we found that the dinitroso tautomers are more stable than the nitroso-hydroxy (NH) ones. This preference is well-interpreted in terms of tautomerization process and nitrosamine resonance. Furthermore, the nature of O-H···O intramolecular hydrogen bond (IMHB), in chelated forms of NH (NH-11 and NH-13) was comprehensively studied to evaluate the effect of hetero atoms (N) on the characteristic of IMHB systems. According to the results of isodesmic reaction method, the hydrogen bond energy of NH-11 is greater than the malonaldehyde (MA) and NH-13, whereas the electron density analysis and energy-geometry correlation methods clearly predict that the hydrogen bond of NH-11 is weaker than the MA. Additionally, the geometrical, atoms in molecules (AIM) and natural bond orbital's (NBO) parameters also emphasize on the MA as a chelated form with the strongest hydrogen bond. Finally, the solvent effects on the relative stability of selected dinitrosamine conformers are evaluated by different continuum (polarizable-continuum model, isodensity polarizable continuum model, and self-consistent isodensity polarizable continuum model), discrete and mixed solvent models. Theoretical results readily show that the potential energy surface of dinitrosamine, especially global minima, is strongly affected by the solvent.