Abstract
The 1H y 13C-NMR spectra of some 1,3 and 1,2,3-trisubstituted 1H-4,5-dihydroimidazolium salts are analyzed.
Introduction
1H-4,5-Dihydroimidazolium salts are typical cyclic amidinium compounds where the cation is resonance stabilized and the positive charge can be delocalized either on the nitrogen atoms or on the C2:
NMR spectra analysis and its comparison with the corresponding saturated compounds (imidazoli-dines 2), allows to reach conclusions about the contribution of such structures.
Experimental
1H and 13C NMR spectra were recorded on a Bruker MSL-300 spectrometer using deuterochloro-form as the solvent.
Results and Discussion
The 1H and 13C-NMR spectroscopic study of a series of 1,3-di and 1,2,3-trisubstituted 1H-4,5-dihydroimidazoliom salts 1 (Table) is presented.
Table 1.
| R1 | R2 | R3 | X- |
| C6H5 | H | C6H5 | Cl- |
| p-CH3C6H4 | H | p-CH3C6H4 | Cl- |
| p-Cl-C6H4 | H | CH2-C6H5 | Cl- |
| C6H5 | C6H5 | CH3 | I- |
| p-CH3C6H4 | C6H5 | CH3 | I- |
| p-CH3OC6H4 | C6H5 | CH3 | I- |
| p-NO2C6H4 | C6H5 | CH3 | I- |
In order to assign the heterocyclic hydrogens and carbons in the 1,2-diaryl-3-methyl substituted compounds, the spectroscopic study of the parent 1H-4,5-dihydroimidazoles 3 and their salts 4 had been carried out.
The unequivocal assignment of the hydrogen and carbon signals of the 1,2,3-trisubstituted salts has been done by the HMQC and HMBC spectra.
The important electronic deficit at the level of the heterocyclic ring in compounds 1 has been clearly demonstrated by comparison of the spectroscopic features of the salts 1 with the corresponding imidazolidines 2. The iminium structure contribution (A,C) was analyzed according to the chemical shifts and the heteronuclear 1J13C-H coupling constants of the heterocyclic ring carbons and N-CH3.