HYDROGEN-BOND DONATION PROPERTIES OF ORGANIC-SOLVENTS AND THEIR AQUEOUS MIXTURES FROM C-13 NMR DATA OF PYRIDINE-N-OXIDE

Measurements of the C-13 nmr chemical shifts delta of pyridine-N-oxide as a probe in 18 solvents, with literature values for others, established that the differences d24 and d34 of the delta of carbons 2 and 3 with respect to that of carbon 4 depend solely on the hydrogen bond donation ability of the solvents, as measured by the Taft-Kamlet alpha parameter. This substance and method can, therefore, be used as an effective probe for alpha, without the need to invoke other solvent properties, such as their polarities/polarizabilities, measured by pi*, required by other probes. The probe was applied also to aqueous mixtures of acetone, acetonitrile, and methanol (values of pi* and beta for acetone, besides those of alpha, being reported here too) with similar results. The two aqueous aprotic solvent mixtures exhibit microheterogeneity, as previously established for aqueous acetonitrile from other results.