ABSTRACT
Heteroaromatic N-oxides contain a donative bond from nitrogen to oxygen and thus a formal positive charge on the first atom. The first important characteristic of heteroaromatic N-oxides is their aromaticity. The dipole moments of many heteroaromatic N-oxides have been derived either from measurements of dielectric constants in solution or from microwave spectra. The nuclear magnetic resonance spectra of heterocyclic N-oxides for all the nuclei concerned give both useful information on the electronic structure and indications for identification. N-oxidation causes characteristic changes in the physical properties of nitrogen heterocycles, and practically all spectroscopic techniques are used for the identification and quantitative analysis of N-oxides. Heterocyclic N-oxides are weakly associated in solution through a dipole-dipole interaction. Hydroxylic acids strongly associate with N-oxides. More important is intermolecular association through hydrogen bonding for compounds containing acidic functions, e.g., alcohols, phenols, and carboxylic acids, or N-hydroxylated derivatives such as 1-hydroxyimidazole 3-oxide.
