Detection of hydrogen bonding in solution: A 2H nuclear magnetic resonance method based on rotational motion of a donor/acceptor complex

Abstract

The effect of hydrogen bonding on the rotational correlation time of an H-bond acceptor, pyridine N-oxide-d₅, in various solvents was investigated using the ²H spin–lattice relaxation time (T₁). The results demonstrate a linear relationship between viscosity and measured rotational correlation times, an example of Stokes–Einstein–Debye behavior. The results also clearly demonstrate reduced rotational rates for the probe in hydrogen bonding solvents in comparison to solvents incapable of forming hydrogen bonds with the probe. The utility of this observation was exploited to estimate the association constant (K_a) through an NMR titration procedure. These results are presented as a new technique that can be applied to the characterization of hydrogen bonding in similar systems.