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

Hindered pyramidal inversion and restricted rotation in N-propyl-N-(4-pyridyl)-1-amino-1H-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 (ΔG, ΔH, and ΔS). 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.