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	tautomer. The Columbia Encyclopedia, Sixth Edition. 2001-05
		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.
	www.bartleby.com /65/ta/tautomer.html (173 words)

	Spartanburg SC \| GoUpstate.com \| Spartanburg Herald-Journal
		Tautomerism is a special case of structural isomerism and can play an important role in non-canonical base pairing in DNA and especially RNA molecules.
		Ring-chain tautomerism occurs when the movement of the proton is accompanied by a change from an open structure to a ring, such as the aldehyde and pyran forms of glucose.
		Valence tautomerism requires a change in molecular geometry and should not be confused with canonical resonance structures or mesomers.
	www.goupstate.com /apps/pbcs.dll/section?category=NEWS&template=wiki&text=Tautomerism (350 words)

	Constant pH Molecular Dynamics with Proton Tautomerism -- Khandogin and Brooks 89 (1): 141 -- Biophysical Journal
		FIGURE 1 Acid-base and proton tautomeric equilibria of histidine (A) and aspartic acid (B).
		In the case of the deprotonated tautomerism (Fig.
		In the case of the protonated tautomerism (Fig.
	www.biophysj.org /cgi/content/full/89/1/141 (7071 words)

	tautomer - Encyclopedia.com
		Recently, the tautomeric equilibria of nucleic acid bases were...
		fluorescence band to the emission from the tautomeric species generated by an excited-state...
		possibility of stabilization as the 5 H tautomeric form (3c and 4) which leads to strong...
	www.encyclopedia.com /doc/1E1-tautomer.html (935 words)

	Keto-Enol Tautomerism
		The Keto-Enol Tautomerism of 2,4-Pentanedione and Related Compounds
		The keto-enol tautomerism of 2,4-pentanedione is a common experiment in many undergraduate physical chemistry courses (1,2).
		In this experiment, the student monitors the relative amount of the tautomers using NMR spectroscopy and the equilibrium constant (keto <==> enol) can then be calculated for the reaction.
	www.thecatalyst.org /experiments/Anderson/Anderson.html (896 words)

	T to Z
		The grouping Y may itself be a three-atom (or five-atom) chain extending the conjugation, as in
		The double bond between Y and Z may be replaced by a ring, when the phenomenon is called ring-chain tautomerism, as in
		See also ambident, sigmatropic rearrangement, tautomerization, valence tautomerization.
	www.chem.qmul.ac.uk /iupac/gtpoc/TtZ.html (1773 words)

	Tautomerism
		The carbon skeleton of the compound is unchanged.
		A reaction which involves simple proton transfer in an intramolecular fashion is called a tautomerism.
		Keto-enol tautomerism is a very common process, and is acid or base catalysed.
	www.chem.ox.ac.uk /vrchemistry/nor/notes/tautomers.htm (99 words)

	Tautomerism and Expert Systems in Spectroscopy Part I: The Problem, Ramification for Spectral Databases, and Current ...
		Tautomerism and Expert Systems in Spectroscopy Part I: The Problem, Ramification for Spectral Databases, and Current Solutions
		Because tautomers often cannot be isolated as single isomers, spectroscopists should always anticipate possible tautomeric forms that can complicate the interpretation of their spectra.
		This involves the use of spectral databases and tautomerically enabled search algorithms, which are reviewed here.
	www.acdlabs.com /publish/publ04/tautomerism.html (93 words)

	Tautomer Summary
		Tautomerism is a special case of structural isomerism and can play an important role in non-canonical base pairing in DNA and especially RNA molecules.
		Prototropic tautomerism refers to the relocation of a proton, as in the above examples, and may be considered a subset of acid-base behavior.
		Ring-chain tautomerism occurs when the movement of the proton is accompanied by a change from an open structure to a ring, such as the aldehyde and pyran forms of glucose.
	www.bookrags.com /Tautomer (692 words)

	Tautomer - Wikipedia, the free encyclopedia
		Tautomerism is a special case of structural isomerism and can play an important role in non-canonical base pairing in DNA and especially RNA molecules.
		Prototropic tautomerism refers to the relocation of a proton, as in the above examples, and may be considered a subset of acid-base behavior.
		Ring-chain tautomerism occurs when the movement of the proton is accompanied by a change from an open structure to a ring, such as the aldehyde and pyran forms of glucose.
	en.wikipedia.org /wiki/Tautomerism (365 words)

	ChemTeam: G.N. Lewis & The Covalent Bond
		In such cases we have the phenomena of tautomerism, where two or more foms of the molecule pass readily into one another and exists together in a condition of mobile equilibrium.
		Tautomerism is not characteristic of organic substances, but is, on the other hand, a predominate trait of most inorganic substances, which behave as if a great variety of forms were existing to gether in extremely mobile equilibrium.
		Like a double bond it may break one bond, producing two odd carbon atoms, but it may also break in a way in which the double bond cannot, to leave a single bond and two carbon atoms (bivalent), each of which has a pair of electrons which is not bound to any other atom.
	dbhs.wvusd.k12.ca.us /webdocs/Chem-History/Lewis-1916/Lewis-1916.html (6968 words)

	ECCC3 Paper 37 (Site not responding. Last check: )
		The tautomerism of 3 and its derivatives is even less well studied; certainly alkylation and acylation yield 1-OR derivatives [7] suggesting 3a, but this is not conclusive, as kinetics or thermodynamics may render alkylation favourable or unfavourable regardless of tautomer prevalence.
		The alternative AM1-SM1a model which requires explicit declaration of atom type, suggested by Cramer and Truhlar for the calculation of heterocyclic tautomerism [28], was not used because of the ambiguous hybridisation of certain atoms in the set, particularly with respect to anions.
		The literature experimentally-based predictions of the tautomerism of 3-, 5-, and 6- hydroxy-pyridazine 1-oxides 2, 4, 5 are confirmed by theory.
	www1.elsevier.com /homepage/saa/eccc3/paper37 (4093 words)

	Keto-enol tautomerism - Wikipedia, the free encyclopedia
		In organic chemistry, keto-enol tautomerism refers to a chemical equilibrium between a ketone or aldehyde (the keto form) 1 and an enol 2.
		Furthermore, the deprotonated intermediate in the interconversion of the two forms, referred to as an enolate anion, is important in carbonyl chemistry, in large part because it is a strong nucleophile.
		One of the early investigators into keto-enol tatomerism was Richard August Carl Emil Erlenmeyer and his Erlenmeyer Rule (1880) states that all alcohols in which the hydroxyl group is attached directly to a double-bonded carbon atom become aldehydes or ketones.
	en.wikipedia.org /wiki/Keto-enol_tautomerism (466 words)

	Enol Summary
		This is tautomerism, where two isomers exist in dynamic equilibrium with each other.
		This tautomerism is brought about by the reversible move of one hydrogen atom.
		Enols are the tautomeric isomers of certain ketones Enolates are the conjugate bases of enols and are important intermediates in both synthetic and biosynthetic chemistry, where the act as nucleophiles in many different substitution reactions..
	www.bookrags.com /Enol (802 words)

	[No title] (Site not responding. Last check: )
		Watson and Crick hypothesized that DNA mutations may be due to tautomerism within the bases, so it is interesting to study the tautomerism of pyrimidine-type bases.
		Tautomerism can be studied with infared spectroscopy in conjunction with theoretically determined infared spectra.
		We can describe the tautomerism by generating a potential energy surface which shows the potential energy as a function of the hydrogen atom's position.
	www.chem.arizona.edu /~smithd/frequencies.html (364 words)

	E-Allen
		The problem of determining the tautomeric behaviour of heterocyclic compounds is a complex one, and many different methods have been employed.
		The determination of heterocyclic tautomerism is an extensive and interesting study in its own right, as well has having relevance to the study of the bioactivity and function of systems based on such heterocycles.
		Our work has been to study the tautomerism of the dioxo-pyrdazines (six membered aromatic rings with adjacent nitrogen heteroatoms, disubstituted with oxygen).
	anusf.anu.edu.au /annual_reports/annual_report97/E-Allan.html (383 words)

	Chem 569
		In this experiment, AM1 and AM1 -SM2 semi-empirical calculations are used to investigate the tautomeric equilibrium involving 2-hydroxypyridine and 2-pyridone both in the gas phase and in water.
		The mechanism of acid catalysis involves protonation at the carbonyl oxygen followed by deprotonation either at the a carbon, leading to the enol tautomer, or at oxygen, leading back to the original keto form.
		You need to assume that there are no significant barriers to the proton transfer reactions in solution, and that the intermediate ions (enolate in the case of base catalysis and protonated acetaldehyde in the case of acid catalysis) represent the "top" of the reaction energy profiles.
	www.siue.edu /CHEMISTRY/eilers/projects/final-project.html (1348 words)

	The Combined Chemical Dictionary Help Index
		The general principles which have been followed are described here using as an illustration one of the commonest types of tautomerism exhibited by simple organic compounds, which is heterocyclic NH OH prototropy as exemplified by 2- and 4-hydroxypyridines.
		Entries often give a statement about tautomerism for a particular compound with supporting reference(s), but in many cases the individual compound will not have been studied closely and the probable tautomerism will have to be inferred.
		All synonyms applicable to the tautomeric forms are given at the head of the entry.
	www.chemnetbase.com /help/ccdhelp/ccdindex.htm (4104 words)

	Amazon.com: tautomerism (Site not responding. Last check: )
		Ring-chain tautomerism of 2-hydroxyethyl carboxylic esters (University of Hawaii) by Pilar Ambrosio Carmelo (Unknown Binding - 1965)
		The tautomerism of oxymethylene and formyl compounds (McGill University.
		Ring-chain tautomerism of the Î² - (p-bromobensoyl)-crotonic esters, (Contribution) by Robert Eliot Lutz (Unknown Binding - 1934)
	www.amazon.com /s?ie=UTF8&keywords=tautomerism&tag=lexico&index=blended&link_code=qs&page=1 (695 words)

	RUI
		RUI: The Role of Solvent Density and Solvation on the Enol-Keto Tautomerism in Supercritical Fluid Solvents
		The density of solvent will be adjusted by varying the temperature and pressure to investigate the effect of density on enol-keto tautomerism, 2) The role of solvation will also be investigated by comparing the tautomeric equilibrium constants in supercritical carbon dioxide with those in supercritical ethane.
		The quadrapole moment for carbon dioxide may lead to a chemical interaction with solutes (mono- and bicarbonyl compounds), 3) Theoretical tautomeric equilibrium constants in SCF solvent will be determined by using the lattice fluid hydrogen bonding model.
	www.ua.edu /academic/colleges/engineering/ei/epscor/rui_solvent.htm (347 words)

	Tautomers/Tautomerism (Site not responding. Last check: )
		In part, tautomers are "isomers that are rapidly interconverted." Frequently, however, the less stable of two tautomers is the important on terms of a compound's ability to exhibit a particular sort of chemical reactivity.
		If one does not recognize the intermediacy of tautomeric forms in such cases, the nature of the reaction will be obscured.
		Primarily because of the much greater strength of a carbonyl double bond as compared with an alkene double bond, the keto form is usualy the more stable of the two.
	www.personal.psu.edu /faculty/t/h/the1/tautomer.htm (155 words)

	Tautomerism as a Constraint on the Composition of Alternative Nucleotide Alphabets
		Tautomerism as a Constraint on the Composition of Alternative Nucleotide Alphabets
		Quantum chemical simulations at the PM3 semi-empirical level of approximation are employed to examine the stability of different tautomeric forms of candidate letters.
		The results suggest that tautomeric instability favoring hydroxyl elements over keto groups is one of the critical constraints on viable alternative alphabets.
	www.alife.org /alife8/abstracts/sub3188 (202 words)

	Keto-Enol Tautomerism of Dimedone Studied by Dynamic NMR (Site not responding. Last check: )
		The keto-enol tautomeric equilibrium of dimedone has been investigated by high-resolution 13C NMR spectroscopy.
		Kinetic information of the solution keto-enol tautomerism for dimedone in DMSO, in the temperature range of 25-85 deg.
		The data are discussed in terms of the different motional environments that result from the geometric restrictions imposed by hydrogen bonding in the crystal structure
	www.s-a-s.org /journal/96/asv50n11/ASv50n11_mr5.html (143 words)

	tautomerism - OneLook Dictionary Search
		Tip: Click on the first link on a line below to go directly to a page where "tautomerism" is defined.
		Tautomerism : Online Plain Text English Dictionary [home, info]
		It is a special case of metamerism; thus, the lactam and the lactim compounds exhibit tautomerism.
	www.onelook.com /?w=tautomerism (231 words)

	Nucleic Acids
		Note that this tautomerism reverses the hydrogen bonding behavior of the nitrogen and oxygen functions (the N-H group of the pyridone becomes a hydrogen bond donor and the carbonyl oxygen an acceptor).
		Similar data for the N-methyl derivative, which cannot tautomerize to a pyridine derivative, is presented on the right.
		Once they had identified the favored base tautomers in the nucleosides, Watson and Crick were able to propose a complementary pairing, via hydrogen bonding, of guanosine (G) with cytidine (C) and adenosine (A) with thymidine (T).
	www.cem.msu.edu /~reusch/VirtualText/nucacids.htm (6250 words)

	Perkin Transaction 2 Articles
		The occurrence of ring—chain tautomerism has been examined in these acids by IR and NMR spectroscopic methods.
		The substituted benzoyl acids are predominantly in the chain (normal) form and the Hammett reaction constants have been used to study the transmission of polar effects in these systems.
		The results for ring-chain tautomerism in acyl carboxylic acids employing a comprehensive series of linking groups are discussed in terms of stereochemistry and steric
	www.rsc.org /Publishing/Journals/P2/article.asp?doi=P29960001921 (131 words)

	Answers to Fourth Examination
		Tautomerism is a change in charge distribution that alters the pattern of pairing of the nucleotide bases in double helical DNA.
		Any of the four bases can be affected, and either type of change can result in GT or AC base pairing.
		Tautomerism appears to be the source of most spontaneous transition mutations.
	www.colorado.edu /MCDB/MCDB2150Fall/exams/examkey9804.html (2036 words)

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