Hindered Inversion/Rotation in Diheteroaryl Alkyl Amines with a N-(1-Pyrazolyl) Group: Dynamic NMR and Molecular Modelling Studies

Abstract

Hindered pyramidal inversion and restricted rotation in N-propyl- N-(4-pyridyl)-1-amino-1 H-pyrazoles were studied by dynamic NMR spectroscopy and molecular modelling. From lineshape analyses of two sets of signals by 1H NMR, thermodynamic parameters were obtained (Δ G, Δ H, and Δ S). The molecular modelling studies allowed us to assign the contribution of both nitrogen inversion (12.3 kcal mol −1) and N–C rotation (2.7 kcal mol −1) to the enthalpy of the energetic barrier.