Benzimidazole
-and benzotriazole-amino derivatives of prog2enoic acid were studied by 'H NMR spectroscopy in the liquid state and by "C NMR spectroscopy in the liquid and solid states. The spectra shows tautomerism of the benzimidazole and benzotriazole rings, E-2 isomerism of the double bond of the propenoic acid substituent and the conformation around the amino -NH-CH-bond. The formation of an intramolecular hydrogen bond between the amino proton and the COOR group of propenoic acid is discussed. The structures of the derivatives are presented on the basis of the I3C CP-MAS NMR spectra in the solid state. KEY WORDS 'H and 13C NMR Benzazoles Prop-2-enoic acid derivatives Solid-and liquid-state structures Compound X Position of R Y 2 l a CH 4 COOEt COOEt l b CH 5 COOEt COOEt lc N Id N 2a CH 2b CH 2c N 2d N 3a CH 3b CH 3c N 3d N 4 5 4 5 4 5 4 5 4 5 COOEt COOEt COOMe COOMe COOMe COOMe CN CN CN CN COOEt COOEt CN CN CN CN CN CN CN CN
We have also undertaken a CP-MAS study, which helps in the understanding of the properties of the derivatives in the liquid state.
The syntheses of the studied compounds (apart from 4-6) have been reported elsewhere.',
EXPERIMENTAL
'H NMR spectra were recorded on a Varian VXR-300 NMR spectrometer for 0.1 M solutions in DMSO-d, in 5 mm 0.d. tubes at 299.9 MHz. A spectral width of 4 kHz was chosen with 32K data points, using a 45" flip angle. The temperature was 294 K and HMDS was used as the internal standard. The I3C NMR spectra in the liquid state were recorded on a JEOL FX 100 FT NMR spectrometer operating at 25.047 MHz for saturated solutions in DMSO-d, at 294 K in 10 mm 0.d. tubes. The spectral width was 6 kHz with 8K data points, which corresponds to a resolution of 1.46 Hz per point. The WALTZ 16 decoupling s e q ~e n c e ' ~ was used. Proton coupled spectra were also recorded, with a 45" pulse and a repetition time of 4 s. The chemical shifts were referenced to the central peak of at 39.5 ppm.