Possibilities of multinuclear NMR in determination of acidity of heteropoly acid solutions

The 1 4 N and 1 3 C NMR parameters of the acidity indicator ortho-nitroaniline (o-NA) and the 1 4 N and 1 7 O NMR parameters of substrates in solutions of some acids and heteropoly acids (HPA) have been measured. The 1 4 N and 1 3 C NMR parameters of Hammet acidity indicators and the 1 4 N and 1 7 O NMR parameters of anions and a solvent depend on the acidity of a solution. The NMR signals of the amino nitrogen atom and the carbon atom bearing the amino group are most sensitive. Comparison of the NMR parameters of the Hammet indicator o-NA in solutions of acids and HPAs shows that the interaction of HPAs with o-NA, which is not related to acidity, additionally contributes to the NMR parameters of o-NA in HPA solutions. It has been shown that the acidity of a water-containing solution can be estimated based on the 1 7 O NMR parameters of water.