Computational studies of the structure of aldazines and ketazines: Part 2. Halogen and α,β-unsaturated derivatives

Photodegradation of Hydrophobic Pyridineketoximes in Toluene and Heptane

The goal of the research was to study the reactivity of the hydrophobic 2- and 3-pyridineketoximes under exposure to UV-VIS light. The photodegradation was conducted in both toluene and heptane for 10 h under atmosphere of argon. Ten-hour irradiation experiments demonstrated that the pyridineketoximes underwent the facile E-Z photoisomerization, photo-Beckmann rearrangement, and to a lesser extent, the photosubstitution to the pyridine ring. From LC-MS and NMR analysis of the irradiated solutions, it was found that the photosubstitution proceeded to give the corresponding 6-substituted 2- or 3-pyridylketoxime via the replacement of the ring hydrogen by the benzyl or heptyl group. The photo-Beckmann rearrangement led to the formation of the corresponding amides, but also other products formed in the photo-decomposition reaction.

The structures of two aldazines: [1,1'-(1E,1'E)-hydrazine-1,2-diylidenebis(methan-1-yl-1-ylidene)dinaphthalen-2-ol] (Lumogen) and 2,2'-(1E,1'E)-hydrazine-1,2-diylidenebis(methan-1-yl-1-ylidene)diphenol (salicylaldazine) in the solid state and in solution

A combination of NMR spectroscopy and theoretical methods Density functional theory including dispersion corrections (DFT-D) was used to study the structures of Lumogen and salicylaldazine. In the solid state, Lumogen exists as the dihydroxy tautomer 1a (an azine, C=N-N=C) as was already known from an X-ray determination. In a deuterated dimethyl sulfoxide solution, another tautomer is observed besides 1a; its structure corresponds to the hydroxy-oxo tautomer 1b (a hydrazone, C=N-NH-Csp(2)). In what concerns salicylaldazine, we have observed only the dihydroxy tautomer 2a.

The structure of azines derived from C-formyl-1H-imidazoles in solution and in the solid state: tautomerism, configurational and conformational studies

The structures of three azines derived from 2-formylimidazole, 4(5)-formylimidazole, and 4(5)-formyl-5(4)-methylimidazole have been determined in solution and in the solid state. Density Functional Theory (DFT) Polarizable Continuum Model (PCM) calculations (geometries, energies, and chemical shifts), NMR [solution and cross polarization magic-angle spinning (CPMAS)], and X-ray crystallography [azine of 4(5)-formylimidazole] have been used. The configuration around the central C = N bonds has been determined and some insights about prototropic tautomerism and conformation have been gained.

Experimental measurements and theoretical calculations of the chemical shifts and coupling constants of three azines (benzalazine, acetophenoneazine and cinnamaldazine)

Three azines, two of them doubly labeled with (15)N, have been studied by multinuclear magnetic resonance in solution and in the solid state. The spectral parameters obtained by iterative analyses have been compared with DFT/B3LYP calculated values (absolute shieldings and coupling constants). The agreement is generally good. Some anomalies have been discussed in relation to the structure of these compounds.