Correlations between the 1H NMR chemical shieldings and the pKa values of organic acids and amines

Correlation between the pKa and nuclear shielding of α-hydrogen of ketones

The α-H acidity is an important chemical property of ketones that has attracted much research interest. Theoretical prediction of pK_a for ketone α-H is significant. In this work, we theoretically studied the nuclear shielding of various α-Hs in a set of ketones and that of the corresponding enolic hydroxyl Hs in tautomeric enol forms. It has been demonstrated through linear regression analyses that the pK_a values of these ketones correlate with both sets of the calculated nuclear shielding values. The correlation coefficient R² of the linear correlation relationship is 0.90. The present work has provided a new approach to computationally evaluating the acidity of α-Hs in ketones, enabling us to semi-empirically predict the ketone α-H acidity from the calculated nuclear shielding values. Graphical AbstractExperimental pK_a values in DMSO vs predicted pK_a values calculated from ¹H nuclear shielding for the hydroxyl hydrogens in the enol forms and for the α-Hs in the keto forms. The surrounding solvent effects were modelled by keto/enol-DMSO clusters and SMD solvent models.