NMR Method for the Determination of Solute Hydrogen Bond Acidity

摘要

It is shown that the difference in the ~1H NMR chemical shift of a protic hydrogen in DMSO and CDCl_3 solvents is directly related to the overall,or summation,hydrogen bond acidity for a wide range of solutes.This provides a new and direct method of measuring the hydrogen bond acidity.For 54 compounds,the observed shifts for 72 protic hydrogens could be correlated to the Abraham solute hydrogen bond acidity parameter,A,with a correlation coefficient squared,R~2,of 0.938 and a standard deviation,SD,of 0.054 units in A.A training equation that used half the data could predict A values for the remaining data with an average error of 0.001 and a standard deviation,SD,of 0.053 units,thus demonstrating the predictive power of the method.Unlike any previous method for the determination of solute hydrogen bond acidities,the NMR method allows the determination of A values for individual protic hydrogens in multifunctional solutes.