Structural characteristics of 1,4-dihydropyridines influencing the nonequivalence of the diastereotopic methylene protons in substituents at positions 2 and 6 were studied. The combined effect of magnetically anisotropic groups and intramolecular hydrogen bonds leads to a considerable difference in the chemical shifts of the methylene protons of the AB system. The unusual reversible temperature evolution of these proton signals in monocyclic 1,4-dihydropyridines is associated with two simultaneous conformational processes. It was estimated that the energetically most favorable conformations are stabilized by an intramolecular CH...O hydrogen bond.
- NMR spectroscopy
- hydrogen bond
- nonequivalence of methylene protons
- quantum-chemical calculations
Field of Science*
- 1.4 Chemical sciences
- 1.1. Scientific article indexed in Web of Science and/or Scopus database