Chem. [f. Gr. ταύτο-, TAUTO- + μέρος part, after ISOMERISM; rendering Ger. tautomerie (Laar, 1885).] The property exhibited by certain organic compounds of behaving in different reactions as if they possessed two (or more) different constitutions, that is, as if the atoms of the same compound or group were arranged in two (or more) different ways, expressible by different structural formula (e.g., the group —CH:C(OH)—, or —CH2.CO—, in ethyl aceto-acetate). So Tautomer, any one of the forms of a tautomeric compound in relation to another; Tautomeric a., pertaining to or exhibiting tautomerism; Tautomery [ad. Ger. tautomerie], = tautomerism.
1885. Conrad Laar, in Ber. Dtsch. Chem. Ges., XVIII. 652. Um die gegenseitige Beziehung gleichberechtigter Formeln … kurz bezeichnen zu können, schlage ich hierfür den Ausdruck ‘Tautomerie’ vor.]
1886. trans. Richter’s Organic Chem. (1899), I. 55. Laar … assumes that such compounds consist of a mixture of structural isomerides, in that an easily mobile hydrogen atom oscillates between two positions in equilibrio, and thereby the entire complex becomes mobile. He designates the phenomenon as tautomery.
1890. Goldschmidt & Meissler, in Jrnl. Chem. Soc., LVIII. 499. Assuming that in the reactions of tautomeric compounds which take place under the influence of electrolytes, the intramolecular change is brought about by the free ions.
1890. Nef, ibid., 983. A discussion of the alleged cases of tautomerism in ethyl succinosuccinate and analogous compounds.
1901. Dixon, ibid., LXXIX. 543. Hitherto no isomerism (or tautomerism) has been established amongst mineral derivatives analogous to that subsisting between the normal and isothiocyanates of organic radicles.
1903. Amer. Chem. Jrnl., May, XXIX. 406. It [thio-urea] may react with the metal [silver] to form a sulphide, or its tautomer may form an insoluble silver compound. Ibid. (1904), Dec., 606. There are ten possible tautomeric formulas for this phenylacetylurazole, and four possible positions for the acetyl group.
1905. Walker, Chem. Soc. Annual Rep., 9. It is suggested that an absorption band appears wherever there is tautomeric change within the molecule.
