Intramolecular hydrogen bonds in 1,4-dihydropyridine derivatives

Abstract

1,4-Dihydropyridine (1,4-DHP) derivatives have been synthesized and characterized by1H,13C,15N nuclear magnetic resonance (NMR) spectroscopy, secondary proton/deuterium13C isotope shifts, variable temperature1H NMR experiments and quantum-chemical calculation. The intramolecular hydrogen bonds NH···O=C andCH···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 the15N nuclear magnetic resonance signals, the shift to the higher wavenumbers of the NH stretching vibration in the infrared spectra and the increase of the1 J(15N,1H) values may indicate the shortening of the N–H bond length upon intramolecular NH···O=C hydrogen bond formation.