NMR Quantification of Hydrogen-Bond-Accepting Ability for Organic Molecules

The hydrogen-bond-accepting abilities for more than 100 organic molecules are quantified using F-19 and P-31 NMR spectroscopy with pentafluorobenzoic acid (PFBA) and phenylphosphinic acid (PPA) as commercially available, inexpensive probes. Analysis of pyridines and anilines with a variety of electronic modifications demonstrates that changes in NMR shifts can predict the secondary effects that contribute to H-bond-accepting ability, establishing the ability of PFBA and PPA binding to predict electronic trends. The H-bond-accepting abilities of various metal-chelating ligands and organocatalysts are also quantified. The measured Delta delta(P-31) and Delta delta(p)(F-19) values correlate strongly with Hammett parameters, pK(a), of the protonated HBA, and proton-transfer basicity pK(BH+)).

Automated summary

By utilizing F-19 and P-31 NMR spectroscopy, the hydrogen-bond-accepting abilities of over 100 organic molecules can be quantified using PFBA and PPA as probes. Analysis indicates that changes in NMR shifts can predict contributions to H-bond-accepting ability, and the binding of PFBA and PPA can predict electronic trends.