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If R and R (note equation at top of page) are different substituents, there is a new stereocenter formed at the alpha position when an enol converts to its keto form. Depending on the nature of the three R groups, the resulting products in this situation would be
274:
In the case of ketones, the conversion is called a keto-enol tautomerism, although this name is often more generally applied to all such tautomerizations. Usually the equilibrium constant is so small that the enol is undetectable spectroscopically.
722:(vitamin C) to an enolate. Enediol at left, enolate at right, showing movement of electron pairs resulting in deprotonation of the stable parent enediol. A distinct, more complex chemical system, exhibiting the characteristic of
1539:
1229:
Kündig, E. Peter; Enríquez García, Alvaro; Lomberget, Thierry; Bernardinelli, Gérald (2006). "Rediscovery, Isolation, and
Asymmetric Reduction of 1,2,3,4-Tetrahydronaphthalene-1,4-dione and Studies of Its Complex".
646:
The acid-catalyzed conversion of an enol to the keto form proceeds by proton transfer from O to carbon. The process does not occur intramolecularly, but requires participation of solvent or other mediators.
1000:
In general, enols are less stable than their keto equivalents because of the favorability of the C=O double bond over C=C double bond. However, enols can be stabilized kinetically or thermodynamically.
1131:
Manbeck, Kimberly A.; Boaz, Nicholas C.; Bair, Nathaniel C.; Sanders, Allix M. S.; Marsh, Anderson L. (2011). "Substituent
Effects on Keto–Enol Equilibria Using NMR Spectroscopy".
808:
results from the fact that the phosphorylated compound is "trapped" in the less thermodynamically favorable enol form, whereas after dephosphorylation it can assume the keto form.
680:, where the C=C subunit is part of an aromatic ring. In some other cases however, enediols are stabilized by flanking carbonyl groups. These stabilized enediols are called
1469:
Zhou, Yu-Qiang; Wang, Nai-Xing; Xing, Yalan; Wang, Yan-Jing; Hong, Xiao-Wei; Zhang, Jia-Xiang; Chen, Dong-Dong; Geng, Jing-Bo; Dang, Yanfeng; Wang, Zhi-Xiang (2013-01-14).
1019:. Another stabilizing factor in 1,3-dicarbonyls is intramolecular hydrogen bonding. Both of these factors influence the enol-dione equilibrium in acetylacetone.
685:
672:
Enediols are alkenes with a hydroxyl group on each carbon of the C=C double bond. Normally such compounds are disfavored components in equilibria with
846:
780:
involve the keto tautomer, for example. Naphthalene-1,4-diol exists in observable equilibrium with the diketone tetrahydronaphthalene-1,4-dione.
855:
1313:
1115:
936:
210:
case) and an enol. The interconversion of the two forms involves the transfer of an alpha hydrogen atom and the reorganisation of bonding
776:
represent a kind of enol. For some phenols and related compounds, the keto tautomer plays an important role. Many of the reactions of
1407:
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893:
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1167:
Guthrie, J. Peter; Povar, Igor (2013). "Equilibrium constants for enolization in solution by computation alone".
761:
730:
1274:
1471:"Stable acyclic aliphatic solid enols: synthesis, characterization, X-ray structure analysis and calculations"
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In some compounds with two (or more) carbonyls, the enol form becomes dominant. The behavior of
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984:. Enolates can be trapped by the addition of electrophiles at oxygen. Silylation gives
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738:
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1004:
Some enols are sufficiently stabilized kinetically so that they can be characterized.
623:. A classic example for favoring the keto form can be seen in the equilibrium between
1548:
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1215:
989:
741:. In the Calvin cycle, the ribulose equilibrates with the enediol, which then binds
719:
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1330:
Modern
Enolate Chemistry: From Preparation to Applications in Asymmetric Synthesis
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126:
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1504:
1399:
962:. In the former area, the fixation of carbon dioxide involves addition of CO
192:
deriving from "-ene"/"alkene" and the "-ol". Many kinds of enols are known.
1015:
Delocalization can stabilize the enol tautomer. Thus, very stable enols are
681:
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1110:(2nd ed.). New York: Oxford University Press. pp. 450–451.
1038:
1016:
812:
773:
584:
207:
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692:
229:
980:
Deprotonation of enolizable ketones, aldehydes, and esters gives
252:) often form enols. The reaction involves migration of a proton (
1305:
Advanced
Organic Chemistry: Reactions, Mechanisms, and Structure
1043:
287:
100:
44:
745:. The same enediol is also susceptible to attack by oxygen (O
286:
684:. Such species are important in glycochemistry, e.g., the
615:
connectivity. Deprotonation of organic carbonyls gives the
1051:, another form of ketones and aldehydes in water solutions
1106:
Clayden, Jonathan; Greeves, Nick; Warren, Stuart (2012).
76:, schematic representation of forms (see text regarding
797:
Keto–enol tautomerism is important in several areas of
822:to the enol phosphate ester. Metabolism of PEP to
1266:
1308:(6th ed.), New York: Wiley-Interscience,
643:(2,4-pentanedione), the enol form is favored.
1392:Ullmann's Encyclopedia of Chemical Technology
136:, enol-form at left, "keto" at right; Ex. is
8:
1458:. Oxford University Press. pp. 456–459.
946:The terminus of the double bond in enols is
686:Lobry de Bruyn-van Ekenstein transformation
110:, enol-form at left, keto at right. Ex. is
54:, keto-form at left, enol at right. Ex. is
1540:Enols and enolates in biological reactions
1265:Berg, Jeremy M.; Tymoczko, Stryer (2002).
1011:Diaryl-substitution stabilizes some enols.
1512:
1494:
804:The high phosphate-transfer potential of
1433:Journal of the American Chemical Society
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1232:Angewandte Chemie International Edition
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1066:
749:) in the (undesirable) process called
1169:Journal of Physical Organic Chemistry
7:
27:Organic compound with a C=C–OH group
1390:G. Roscher (2007). "Vinyl Esters".
1194:Schank, Kurt (1972). "Reductones".
954:organic compounds is important in
704:isomers at left and right. Ex. is
180:(R = many substituents). The term
25:
988:. Acylation gives esters such as
937:Carbonyl α-substitution reactions
899:
892:
862:
853:
844:
784:
125:
99:
65:
43:
836:substrate-level phosphorylation
651:Stereochemistry of ketonization
297:Selected enolization constants
698:Keto-enediol tautomerizations.
631:(K = / ≈ 3
214:. The keto and enol forms are
92:, also a less stabilized enol.
1:
1360:Mukaiyama, T.; Kobayashi, S.
818:catalyzes the dehydration of
760:Keto-enediol equilibrium for
1379:10.1002/0471264180.or046.01
960:synthetic organic chemistry
1601:
1454:Clayden, Jonathan (2012).
1273:(5th ed.). New York:
1081:(5th ed.). New York:
1079:Advanced Organic Chemistry
1077:Smith MB, March J (2001).
973:
934:
733:is a key substrate in the
942:Addition of electrophiles
924:
922:
898:
891:
861:
859:
852:
850:
843:
762:ribulose-1,5-bisphosphate
731:Ribulose-1,5-bisphosphate
607:Enols are derivatives of
282:illustrates this effect:
256:) from carbon to oxygen:
202:between a "keto" form (a
58:, a less stabilized enol.
1400:10.1002/14356007.a27_419
1275:W.H. Freeman and Company
1431:"Stable simple enols".
1394:. Weinheim: Wiley-VCH.
970:Deprotonation: enolates
700:Enediol in the center;
676:. One special case is
545:Hexafluoroacetylacetone
206:, named for the common
1565:Reactive intermediates
1328:Manfred Braun (2015).
1244:10.1002/anie.200502588
1085:. pp. 1218–1223.
1012:
950:. Its reactions with
832:adenosine triphosphate
820:2-phosphoglyceric acid
765:
727:
709:
581:Cyclohexa-2,4-dienone
508:Trifluoroacetylacetone
291:
184:is an abbreviation of
118:(---) stabilized enol.
34:Examples of keto-enol
1338:10.1002/9783527671069
1010:
759:
717:
696:
619:, which are a strong
290:
248:bond adjacent to the
196:Keto–enol tautomerism
1208:10.1055/s-1972-21845
200:chemical equilibrium
74:resonance structures
1487:2013NatSR...3E1058Z
1441:10.1021/ja00203a019
1298:Smith, Michael B.;
1146:2011JChEd..88.1444M
806:phosphoenolpyruvate
298:
1575:Alkene derivatives
1475:Scientific Reports
1083:Wiley Interscience
1013:
766:
728:
710:
296:
292:
78:molecular orbitals
1585:Organic reactions
1555:Functional groups
1496:10.1038/srep01058
1456:Organic Chemistry
1315:978-0-471-72091-1
1175:(12): 1077–1083.
1154:10.1021/ed1010932
1140:(10): 1444–1445.
1117:978-0-19-927029-3
1108:Organic chemistry
928:
927:
708:, shown at right.
605:
604:
172:with the formula
170:organic chemistry
154:organic chemistry
88:at right; Ex. is
16:(Redirected from
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1055:Regioselectivity
986:silyl enol ether
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162:Functional group
140:(reductone), an
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112:2,4-pentanedione
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828:pyruvate kinase
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134:tautomerization
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1534:External links
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718:Conversion of
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706:hydroxyacetone
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495:C(O)CH=C(OH)CH
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250:carbonyl group
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160:are a type of
144:-type of enol.
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1002:
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990:vinyl acetate
987:
983:
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967:
961:
957:
953:
952:electrophilic
949:
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720:ascorbic acid
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683:
679:
675:
667:
665:
663:
659:
658:diastereomers
650:
648:
644:
642:
641:acetylacetone
638:
637:1,3-diketones
630:
626:
625:vinyl alcohol
622:
618:
617:enolate anion
610:
609:vinyl alcohol
600:
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471:Acetylacetone
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1300:March, Jerry
1293:
1269:Biochemistry
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1078:
1049:Geminal diol
1014:
1003:
999:
996:Stable enols
979:
966:to an enol.
956:biochemistry
948:nucleophilic
945:
824:pyruvic acid
810:
803:
799:biochemistry
796:
793:Biochemistry
772:
735:Calvin cycle
729:
697:
671:
654:
645:
629:acetaldehyde
606:
426:Acetophenone
317:Acetaldehyde
277:
273:
225:
198:refers to a
195:
194:
190:portmanteaus
185:
181:
166:intermediate
157:
151:
1481:(1): 1058.
1363:Org. React.
958:as well as
662:enantiomers
621:nucleophile
310:enolization
222:Enolization
56:3-pentanone
36:tautomerism
1560:Metabolism
1549:Categories
1061:References
935:See also:
931:Reactivity
834:(ATP) via
778:resorcinol
682:reductones
639:, such as
409:=CH(OH)OCH
242:α-hydrogen
90:2-butanone
1505:2045-2322
1418:241676899
1216:260331550
1196:Synthesis
611:, with a
302:carbonyl
238:aldehydes
216:tautomers
212:electrons
132:Aldehyde
82:carbanion
1570:Alcohols
1523:23320139
1435:. 1989.
1302:(2007),
1252:16304647
1023:See also
982:enolates
724:vinylogy
678:catechol
674:acyloins
668:Enediols
635:10). In
454:C(OH)=CH
368:C(OH)=CH
269:)=CR′R′′
240:with an
204:carbonyl
72:Enolate
1514:3544012
1483:Bibcode
1142:Bibcode
1034:Enolase
1029:Alkenal
1017:phenols
976:enolate
816:enolase
774:Phenols
769:Phenols
702:acyloin
601:>10
348:Acetone
261:RC(=O)C
234:ketones
227:Organic
186:alkenol
142:enediol
106:Ketone
86:enolate
50:Ketone
18:Enediol
1521:
1511:
1503:
1416:
1406:
1344:
1312:
1281:
1250:
1214:
1114:
1089:
1039:Ketone
813:enzyme
613:C=C−OH
585:Phenol
557:C(O)CF
553:C(O)CH
520:C(O)CF
516:C(O)CH
483:C(O)CH
479:C(O)CH
438:C(O)CH
356:C(O)CH
236:, and
230:esters
208:ketone
178:C=CROH
1580:Enols
1414:S2CID
1373:, 1.
1212:S2CID
502:0.27
334:=CHOH
305:enol
158:enols
1519:PMID
1501:ISSN
1404:ISBN
1367:1994
1342:ISBN
1310:ISBN
1279:ISBN
1248:PMID
1200:1972
1112:ISBN
1087:ISBN
1044:Ynol
811:The
627:and
576:~10
375:5.12
188:, a
182:enol
114:, a
1509:PMC
1491:doi
1437:doi
1396:doi
1375:doi
1334:doi
1240:doi
1204:doi
1177:doi
1150:doi
886:ATP
881:ADP
826:by
737:of
660:or
539:32
465:10
420:10
379:10
342:10
338:5.8
325:CHO
246:C−H
168:in
164:or
152:In
80:);
1551::
1517:.
1507:.
1499:.
1489:.
1477:.
1473:.
1412:.
1402:.
1371:46
1369:,
1340:.
1277:.
1246:.
1236:45
1234:.
1210:.
1198:.
1173:26
1171:.
1148:.
1138:88
1069:^
992:.
914:O
877:O
838:.
801:.
753:.
688:.
664:.
597:OH
565:CF
549:CF
528:CH
512:CH
491:CH
475:CH
405:CH
397:CH
393:CO
389:CH
364:CH
352:CH
330:CH
321:CH
232:,
156:,
1525:.
1493::
1485::
1479:3
1443:.
1439::
1420:.
1398::
1377::
1350:.
1336::
1287:.
1254:.
1242::
1218:.
1206::
1183:.
1179::
1156:.
1152::
1144::
1120:.
1095:.
964:2
912:2
910:H
875:2
873:H
764:.
747:2
726:.
633:×
595:5
593:H
591:6
589:C
571:3
567:3
559:3
555:2
551:3
534:3
530:3
522:3
518:2
514:3
497:3
493:3
485:3
481:2
477:3
463:×
461:1
456:2
452:5
450:H
448:6
446:C
440:3
436:5
434:H
432:6
430:C
418:×
416:4
411:3
407:2
399:3
395:2
391:3
377:×
370:2
366:3
358:3
354:3
340:×
332:2
323:3
308:K
267:H
263:H
254:H
244:(
176:2
174:R
20:)
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