NMR Parameters and Geometries of OHN and ODN Hydrogen Bonds of Pyridine–Acid Complexes

Abstract

In this paper, equations are proposed which relate various NMR parameters of OHN hydrogen-bonded pyridine-acid complexes to their bond valences which are in turn correlated with their hydrogen-bond geometries. As the valence bond model is strictly valid only for weak hydrogen bonds appropriate empirical correction factors are proposed which take into account anharmonic zero-point energy vibrations. The correction factors are different for OHN and ODN hydrogen bonds and depend on whether a double or a single well potential is realized in the strong hydrogen-bond regime. One correction factor was determined from the known experimental structure of a very strong OHN hydrogen bond between pentachlorophenol and 4-methylpyridine, determined by the neutron diffraction method. The remaining correction factors which allow one also to describe H/D isotope effects on the NMR parameters and geometries of OHN hydrogen bond were determined by analysing the NMR parameters of the series of protonated and deuterated pyridine- and collidine-acid complexes. The method may be used in the future to establish hydrogen-bond geometries in biologically relevant functional OHN hydrogen bonds.

Geometric H/D Isotope Effects and Cooperativity of the Hydrogen Bonds in Porphycene

“…Limbach et al modified this correlation and obtained a better fit to experimental data, especially in the region of symmetric and quasisymmetric hydrogen bonds (where q 1 is close to 0). [39] Knowing experimental X-ray geometries of porphycene and porphyrin, as well as NÀH distances obtained from dipolar relaxation data, [16] and adapting an experimental model for the NÀH···O hydrogen bond [40] to the NÀ H···N case, we can predict the primary H/D GIE. An established correlation of proton/deuteron chemical shifts and the geometric parameter q 1 [16] made it possible to estimate the secondary H/D GIE as well.…”

A DFT and AIM analysis of the spin–spin couplings across the hydrogen bond in the 2‐fluorobenzamide and related compounds

“…The smaller experimental values can be explained in terms of quantum zero point vibrational effects as proposed previously for NHN [37] and OHN [38] systems. Because of the width of the zero-point vibration of the proton, the real N· · ·F distances are larger in the strong short hydrogen bond regime than the equilibrium distances.…”

Hydrogen bonding in protic ionic liquids: structural correlations, vibrational spectroscopy, and rotational dynamics of liquid ethylammonium nitrate

“…can be described by a single coordinate [62]. This path is commonly plotted into a graph showing the correlation between the coordinates r 1 = 0.5(r NH − r OH ) and r 2 = r NH + r OH .…”