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

The acid dissociation constants and ¹H NMR chemical shieldings of organic compounds are important properties that have attracted much research interest. However, few studies have explored the relationship between these two properties. In this work, we theoretically studied the NMR chemical shifts of a series of carboxylic acids and amines in the gas phase and in aqueous solution. It was found that the negative logarithms of the experimental acid dissociation constants (i.e., the pK_a values) of the organic acids and amines in aqueous solution correlate almost linearly with the corresponding calculated NMR chemical shieldings. Key factors that affect the theoretically predicted pK_a values are discussed in this paper. The present work provides a new way to predict the pK_a values of organic/biochemical compounds. [Figure not available: see fulltext.]