HOME

TheInfoList




Tautomers () are
structural isomer In chemistry, a structural isomer (or constitutional isomer in the IUPAC nomenclature) of a chemical compound, compound is another compound whose molecule has the same number of atoms of each element, but with logically distinct chemical bond, bon ...
s (constitutional isomers) of
chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemical bonds. A homonuclear molecule, m ...
s that readily interconvert. This reaction commonly results in the relocation of a hydrogen atom. Tautomerism is for example relevant to the behavior of amino acids and nucleic acids, two of the fundamental building blocks of life. The concept of tautomerizations is called tautomerism. Tautomerism is also called desmotropism. The
chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and t ...

chemical reaction
interconverting the two is called tautomerization. Care should be taken not to confuse tautomers with depictions of "contributing structures" in chemical
resonance Resonance describes the phenomenon of increased amplitude The amplitude of a Periodic function, periodic Variable (mathematics), variable is a measure of its change in a single Period (mathematics), period (such as frequency, time or Wavelen ...
. Tautomers are distinct chemical species that can be distinguished by their differing atomic connectivities, molecular geometries, and physicochemical and spectroscopic properties, whereas resonance forms are merely alternative
Lewis structure#REDIRECT Lewis structure Lewis structures, also known as Lewis dot formulas, Lewis dot structures, electron dot structures, or Lewis electron dot structures (LEDS), are diagrams that show the bonding between atom An atom is the smallest unit o ...
(
valence bond theory In chemistry, valence bond (VB) theory is one of the two basic theories, along with molecular orbital theory, molecular orbital (MO) theory, that were developed to use the methods of quantum mechanics to explain chemical bonding. It focuses on how ...
) depictions of a single chemical species, whose true structure is best described as the "average" of the idealized, hypothetical geometries implied by these resonance forms.


Examples

Tautomerization is pervasive in
organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and th ...
. It is typically associated with polar molecules and ions containing functional groups that are at least weakly acidic. Most common tautomers exist in pairs, which means that the hydrogen is located at one of two positions, and even more specifically the most common form involves a hydrogen changing places with a double bond: H−X−Y=Z ⇌ X=Y−Z−H. Common tautomeric pairs include: *
ketone In chemistry, a ketone is a functional group with the structure R2C=O, where R can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond). The simplest ketone is acetone (R = R' = methyl) ...
enol Enols, or more formally, alkenols, are a type of reactive structure or chemical intermediate, intermediate in organic chemistry that is represented as an alkene (olefin) with a hydroxyl group attached to one end of the alkene double bond. The term ...

enol
: H−O−C=C ⇌ O=C−C−H, see
keto–enol tautomerism Enols, or more formally, alkenols, are a type of reactive structure or chemical intermediate, intermediate in organic chemistry that is represented as an alkene (olefin) with a hydroxyl group attached to one end of the alkene double bond. The terms ...
*
enamine An enamine is an unsaturated compound derived by the condensation of an aldehyde or ketone with a secondary amine. Enamines are versatile intermediates. : The word "enamine" is derived from the affix ''en''-, used as the suffix of alkene, and the ...

enamine
imine An imine ( or ) is a or containing a – . The nitrogen atom can be attached to a hydrogen (H) or an organic group (R). If this group is ''not'' a hydrogen atom, then the compound can sometimes be referred to as a . The carbon atom has two addi ...

imine
: H−N−C=C ⇌ N=C−C−H **
cyanamide Cyanamide is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, cat ...

cyanamide
carbodiimide In organic chemistry, a carbodiimide (systematic IUPAC name: methanediimine) is a functional group In organic chemistry, a functional group is a substituent or moiety in a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling ...
**
guanidine Guanidine is the compound with the formula HNC(NH2)2. It is a colourless solid that dissolves in polar solvents. It is a strong base that is used in the production of plastics and explosives. It is found in urine Urine is a liquid by-product ...
– guanidine – guanidine: With a central carbon surrounded by three
nitrogens
nitrogens
, a guanidine group allows this transform in three possible orientations *
amide In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a chemical compound, compound with the general formula RC(=O)NR′R″, where R, R', and R″ represent organic compound, organic functional group, groups or ...

amide
imidic acid In chemistry, an imidic acid is any molecule that contains the -C(=NH)-OH functional group. It is the tautomer of an amide and the isomer of an oxime. The term "imino acid" is an obsolete term for this group that should not be used in this context ...
: H−N−C=O ⇌ N=C−O−H (e.g., the latter is encountered during
nitrile A nitrile is any organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior ...
hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution Substitution may refer to: Arts and media *Chord substitution, in music, swapping one chord fo ...

hydrolysis
reactions) **
lactam A lactam is a Cyclic compound, cyclic amide, formally derived from an amino alkanoic acid. The term is a portmanteau of the words ''lactone'' + ''amide''. Nomenclature Greek prefixes in alphabetical order indicate ring size: * α-Lactam (3-atom r ...

lactam
lactim A lactam is a cyclic Cycle or cyclic may refer to: Anthropology and social sciences * Cyclic history, a theory of history * Cyclical theory, a theory of American political history associated with Arthur Schlesinger, Sr. * Social cycle, various c ...
, a cyclic form of amide-imidic acid tautomerism in
2-pyridone 2-Pyridone is an organic compound with the formula . It is a colourless solid. It is well known to form hydrogen bonded dimers and it is also a classic case of a compound that exists as tautomers. Tautomerism The second tautomer is 2-hydroxy ...

2-pyridone
and derived structures such as the
nucleobase 230px, Pyrimidine nucleobases are simple ring molecules. Nucleobases, also known as ''nitrogenous bases'' or often simply ''bases'', are nitrogen-containing biological compounds that form nucleosides Nucleosides are glycosylamines that can be ...
s
guanine Guanine () (symbol A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical me ...

guanine
,
thymine Thymine () (symbol A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical m ...

thymine
, and
cytosine Cytosine () (symbol A symbol is a mark, sign, or that indicates, signifies, or is understood as representing an , , or . Symbols allow people to go beyond what is n or seen by creating linkages between otherwise very different s and s. Al ...

cytosine
* imine – imine, e.g., during
pyridoxal phosphate Pyridoxal phosphate (PLP, pyridoxal Pyridoxal is one form of vitamin B6. Some medically relevant bacteria, such as those in the genera ''Granulicatella'' and ''Abiotrophia'', require pyridoxal for growth. This nutritional requirement can lead ...

pyridoxal phosphate
catalyzed
enzymatic Enzymes () are protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme ...
reactions **R1R2C(=NCHR3R4) ⇌ (R1R2CHN=)CR3R4 *nitro – ''aci''-nitro (nitronic acid): RR'HC–N+(=O)(O) ⇌ RR'C=N+(O)(OH) *
nitroso of nitroso moiety Nitroso refers to a functional group In organic chemistry, a functional group is a substituent or moiety in a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, whic ...
oxime An oxime is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemical b ...
: H−C−N=O ⇌ C=N−O−H *
ketene A ketene is an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, and sy ...

ketene
ynol, which involves a triple bond: H−C=C=O ⇌ C≡C−O−H *
amino acid Amino acids are organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, a ...

amino acid
– ammonium carboxylate, which applies to the building blocks of the proteins. This shifts the proton more than two atoms away, producing a
zwitterionIn chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo ...
rather than shifting a double bond: H2N−CH2−COOH ⇌ H3N−CH2−CO *
phosphite The general structure of a phosphite ester showing the lone pairs on the P In chemistry a phosphite ester or organophosphite usually refers to an organophosphorous compound with the formula P(OR)3. They can be considered as esters of an unobserve ...
phosphonate Phosphonates and phosphonic acids are organophosphorus compound Organophosphorus compounds are organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), mill ...

phosphonate
: P(OR)2(OH) ⇌ HP(OR)2(=O) between trivalent and pentavalent phosphorus.


Prototropy

Prototropy is the most common form of tautomerism and refers to the relocation of a hydrogen atom. Prototropic tautomerism may be considered a subset of
acid-base
acid-base
behavior. Prototropic tautomers are sets of isomeric
protonation In chemistry, protonation (or hydronation) is the addition of a proton (or hydron, or hydrogen cation), (H+) to an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance ...
states with the same
empirical formula In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they underg ...
and total
charge Charge or charged may refer to: Arts, entertainment, and media Films * ''Charge, Zero Emissions/Maximum Speed'', a 2011 documentary Music * Charge (David Ford album), ''Charge'' (David Ford album) * Charge (Machel Montano album), ''Charge'' (Mac ...
. Tautomerizations are
catalyzed that utilizes a low-temperature oxidation catalyst to convert carbon monoxide to less toxic carbon dioxide at room temperature. It can also remove formaldehyde from the air. Catalysis () is the process of increasing the reaction rate, rate of a ...

catalyzed
by: *
base Base or BASE may refer to: Brands and enterprises * Base (mobile telephony provider), a Belgian mobile telecommunications operator *Base CRM Base CRM (originally Future Simple or PipeJump) is an enterprise software company based in Mountain Vie ...
s, involving a series of steps: deprotonation, formation of a delocalized
anion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ...
(e.g., an
enolate Enolates are organic anions derived from the deprotonation of carbonyl compounds. Rarely isolated, they are widely used as reagents in the synthesis of organic compounds. Bonding and structure Enolate anions are electronically related to allyl ...

enolate
), and
protonation In chemistry, protonation (or hydronation) is the addition of a proton (or hydron, or hydrogen cation), (H+) to an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance ...
at a different position of the anion; and *
acid An acid is a or capable of donating a (hydrogen ion H+) (a ), or, alternatively, capable of forming a with an (a ). The first category of acids are the proton donors, or s. In the special case of , proton donors form the H3O+ and are ...
s, involving a series of steps: protonation, formation of a delocalized cation, and deprotonation at a different position adjacent to the cation). Two specific further subcategories of tautomerizations: *Annular tautomerism is a type of prototropic tautomerism wherein a proton can occupy two or more positions of a
heterocyclic 125px, Pyridine, a heterocyclic compound A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different chemical element, elements as members of its ring(s). Heterocyclic chemistry is the branch of organi ...
system, for example, 1''H''- and 3''H''-
imidazole Imidazole is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior ...
; 1''H''-, 2''H''- and 4''H''- 1,2,4-triazole; 1''H''- and 2''H''-
isoindole Isoindole in heterocyclic chemistry Image:Pyridine.svg, 125px, Pyridine, a heterocyclic compound A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different chemical element, elements as members of it ...
. *Ring–chain tautomers occur when the movement of the proton is accompanied by a change from an open structure to a ring, such as the
open chainIn chemistry, an open-chain compound (also spelled as open chain compound) or acyclic compound (Greek prefix "α", ''without'' and "κύκλος", ''cycle'') is a compound with a linear structure, rather than a Cyclic compound, cyclic one. An open-ch ...
and cyclic
hemiacetal A hemiacetal or a hemiketal have the general formula R1R2C(OH)OR, where R1 or R2 is hydrogen or an organic substituent. They generally result from the addition of an alcohol In , alcohol is an that carries at least one (−OH) bound to a ...

hemiacetal
(typically
pyranose Pyranose is a collective term for saccharides that have a chemical structure that includes a six-membered ring consisting of five carbon atoms and one oxygen atom. There may be other carbons external to the ring. The name derives from its similarity ...
or
furanose A furanose is a collective term for carbohydrates is a disaccharide found in animal milk. It consists of a molecule of galactose, D-galactose and a molecule of glucose, D-glucose bonded by beta-1-4 glycosidic linkage. A carbohydrate () is a bio ...
forms) of many sugars. (See .) The tautomeric shift can be described as H−O ⋅ C=O ⇌ O−C−O−H, where the "⋅" indicates the initial absence of a bond.


Valence tautomerism

Valence tautomerism is a type of tautomerism in which single and/or double bonds are rapidly formed and ruptured, without migration of atoms or groups. It is distinct from prototropic tautomerism, and involves processes with rapid reorganisation of bonding electrons. A pair of valence tautomers with formula C6H6O are benzene oxide and
oxepin Oxepin is an oxygen-containing heterocycle consisting of a seven-membered ring (chemistry), ring with three double bonds. The parent C6H6O exists as an chemical equilibrium, equilibrium mixture with benzene oxide. The oxepin–benzene oxide equil ...

oxepin
. Other examples of this type of tautomerism can be found in
bullvalene Bullvalene is a hydrocarbon with the chemical formula C10H10. The molecule has a cage-like structure formed by the fusion of one cyclopropane and three 1,4-Cycloheptadiene, cycloheptadiene rings. Bullvalene is unusual as an organic molecule due to ...

bullvalene
, and in open and closed forms of certain
heterocycle 125px, Pyridine, a heterocyclic compound A heterocyclic compound or ring structure is a cyclic compound A cyclic compound (''ring compound'') is a term for a compound in the field of chemistry Chemistry is the scientific discipline invol ...
s, such as organic
azide Azide is the anion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects tha ...

azide
s and
tetrazole Tetrazoles are a class of synthetic organic heterocyclic compound, consisting of a 5-member ring of four nitrogen Nitrogen is the chemical element with the Symbol (chemistry), symbol N and atomic number 7. It was first discovered and isolated ...
s, or mesoionic münchnone and acylamino ketene. Valence tautomerism requires a change in molecular geometry and should not be confused with canonical
resonance structures In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they und ...
or mesomers.


See also

*
Fluxional molecule Fluxional (or non-rigid) molecules are molecule A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change i ...
*
Favipiravir Favipiravir, sold under the brand name Avigan among others, is an antiviral medication used to treat influenza Influenza, commonly called "the flu", is an infectious disease caused by influenza viruses. Symptoms range from mild to severe ...

Favipiravir


References


External links

*{{Commonscatinline, Tautomerism Isomerism