New stage in the development of anthraquinone chemistry and the structure of alizarin

Chemistry of 9,10-anthraquinones is considered as chemistry of isomeric anthraquinones existing in dynamic equilibrium with each other. Diversity of electronic absorption spectra of the same compounds is determined by tautomeric transformations. Alizarin exists as equilibrium mixtures of tautomers and conformers having 9,10- and 2,9-quinoid structures. Qualitatively different compositions are inherent not only to samples of alizarin prepared or purified by different methods but also to different solvates of the same sample. © Pleiades Publishing, Ltd., 2012.