Molecular structure of di-aryl-aldimines by multinuclear magnetic resonance and X-ray diffraction

The complete H-1, C-13 and N-15 NMR analyses for a series of 25 diaryl-aldimines containing phenyl, pyridyl, pyrazolone and furanyl moieties are described herein. Detailed evaluation of substituent chemical shift and coupling constant effects showed that interaction between the lone pair of the pyrazolone carbonyl group or the nitrogen of 2-substitued pyridines with the aldimine hydrogen increases the (1)J(CH) value and shifts the resonance signal for this hydrogen to high frequency, in the H-1 NMR spectra. The X-ray crystal structure analysis of pyrazolone substituted aldimines evidenced the planarity of the aryl groups which are conjugated with the C=N double bond. In the case of the N-(2-pyridinemethylene)-1,5-dimethyl-2-phenyl-1,2-dihydro-pyrazol-3-one, two rotamers were observed in the same unit cell. (C) 2003 Elsevier B.V. All rights reserved.