1,4-Dihydropyridine (1,4-DHP) derivatives have been synthesized and characterized by 1H, 13C, 15N nuclear magnetic resonance (NMR) spectroscopy, secondary proton/deuterium 13C isotope shifts, variable temperature 1H NMR experiments and quantum-chemical calculation. The intramolecular hydrogen bonds NH⋯O=C and CH⋯O=C in these compounds were established by NMR and quantum-chemical studies The downfield shift of the NH proton, accompanied by the upfield shift of the 15N nuclear magnetic resonance signals, the shift to the higher wavenumbers of the NH stretching vibration in the infrared spectra and the increase of the 1J(15N,1H) values may indicate the shortening of the N-H bond length upon intramolecular NH⋯O=C hydrogen bond formation.
Keywords: 1; 4-dihydropyridines; DFT; H/D 13C isotope effects; IR; NMR; hydrogen bond.