tautomer


Also found in: Dictionary, Medical, Wikipedia.

tautomer

(tô`təmər), one of two or more structural isomersisomer
, in chemistry, one of two or more compounds having the same molecular formula but different structures (arrangements of atoms in the molecule). Isomerism is the occurrence of such compounds. Isomerism was first recognized by J. J. Berzelius in 1827.
..... Click the link for more information.
 that exist in equilibrium and are readily converted from one isomeric form to another. Of the various types of tautomerism that are possible, two are commonly observed. In keto-enol tautomerism a simultaneous shift of electrons and a hydrogen atom occurs; it was first observed by K. Meyer in the ethyl ester of 3-oxobutanoic acid (ethyl acetoacetate), which occurs naturally as a mixture of the two forms. Ring-chain tautomerism, first recognized by Emil Fischer, is exhibited by glucose. It arises as a result of the aldehyde group (-CHO) in a sugar chain molecule reacting with one of the hydroxy groups (-OH) in the same molecule to give it a cyclic (ring-shaped) form.
The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/
References in periodicals archive ?
The ratios were determined through NMR spectroscopic studies by measuring the integral ratios of the CH=N sharp singlets in the solvents reported and the attribution to the two tautomers of the different groups of signals was done upon COSY experiments.
The tautomer state of polymer with-SH group at pH = 2 may activate the reduction reaction for chromate ion.
THEORETICAL STUDY OF TWO TAUTOMERS OF LOSARTAN IN GAS PHASE AND AQUEOUS SOLUTION.
The phenomenon that the [[M + H].sup.+] ion does not exist for DiMMA can be explained by the fact that the a carbon in the DiMMA molecule does not have an active hydrogen that would allow tautomer formation.
Spartan codes enabled identification of tautomers (due to proton transfer) through tautomer search.
The ligands were prepared at pH 7.0 [+ or -] 2.0 using Epik state and the large penalties of high energy ionization or tautomer states were removed.
It has been studied earlier that the presence of ortho hydroxyl group in Schiff bases favours the existence of intramolecular hydrogen bonds and the tautomerism, which accounts for the formation of either phenol-amine or keto-amine tautomer (Scheme 1).
The resulting proton-transfer tautomer is substantially different in structure and electronic configuration from its corresponding ground state, that is, a large Stokes shifted [K.sup.*] [right arrow] K emission.
In tandem, structural modifications of many Schiff bases have been examined by proton nuclear magnetic resonance ([.sup.1]H NMR) and UV-vis spectroscopy, X-ray analysis (20), (21) or fluorescence spectroscopy (22), (23), the latter arguing the formation of keto tautomer accompanied of a large Stokes shift (100 nm).
It is available as freeware, with tools for tautomer prediction, 2-D structure cleaning, 3-D optimization and viewing, drawing of polymers, organometallics and Markush structures.
The NMR data showed the enamine-enamine tautomer of these Schiff bases via characteristic chemical shifts of NH protons resulting from hydrogen bonding formation ranging from 13.34 to 13.49 ppm in the [sup.1]H NMR spectrum [24].
In general the Schiff bases that are derived from salicylaldehyde exist mainly as the enol-tautomer with a variable contribution from the keto-tautomer (depending on the substituents) while those derived from 2- hydroxynaphthaldehyde are dominated by the keto- tautomer structure [5].