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883:
775:
683:
56:
116:
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34:
644:
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
263:
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.
711:(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
1528:
1218:
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".
635:
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.
989:
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.
1120:
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".
797:
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.
669:, 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
1458:
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).
1008:. Another stabilizing factor in 1,3-dicarbonyls is intramolecular hydrogen bonding. Both of these factors influence the enol-dione equilibrium in acetylacetone.
674:
661:
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
835:
769:
involve the keto tautomer, for example. Naphthalene-1,4-diol exists in observable equilibrium with the diketone tetrahydronaphthalene-1,4-dione.
844:
1302:
1104:
925:
199:
case) and an enol. The interconversion of the two forms involves the transfer of an alpha hydrogen atom and the reorganisation of bonding
765:
represent a kind of enol. For some phenols and related compounds, the keto tautomer plays an important role. Many of the reactions of
1396:
1334:
1271:
1079:
853:
1553:
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889:
882:
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1563:
1573:
1543:
1156:
Guthrie, J. Peter; Povar, Igor (2013). "Equilibrium constants for enolization in solution by computation alone".
750:
719:
1263:
1460:"Stable acyclic aliphatic solid enols: synthesis, characterization, X-ray structure analysis and calculations"
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62:
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In some compounds with two (or more) carbonyls, the enol form becomes dominant. The behavior of
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100:
973:. Enolates can be trapped by the addition of electrophiles at oxygen. Silylation gives
843:
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96:
40:
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1502:
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727:
694:
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373:
238:
993:
Some enols are sufficiently stabilized kinetically so that they can be characterized.
612:. A classic example for favoring the keto form can be seen in the equilibrium between
1537:
1406:
1256:
1204:
978:
730:. In the Calvin cycle, the ribulose equilibrates with the enediol, which then binds
708:
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1319:
Modern
Enolate Chemistry: From Preparation to Applications in Asymmetric Synthesis
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609:
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55:
44:
24:
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650:
115:
78:
1493:
1388:
951:. In the former area, the fixation of carbon dioxide involves addition of CO
181:
deriving from "-ene"/"alkene" and the "-ol". Many kinds of enols are known.
1004:
Delocalization can stabilize the enol tautomer. Thus, very stable enols are
670:
226:
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1099:(2nd ed.). New York: Oxford University Press. pp. 450–451.
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1005:
801:
762:
573:
196:
995:
744:
702:
681:
218:
969:
Deprotonation of enolizable ketones, aldehydes, and esters gives
241:) often form enols. The reaction involves migration of a proton (
1294:
Advanced
Organic Chemistry: Reactions, Mechanisms, and Structure
1032:
276:
89:
33:
734:. The same enediol is also susceptible to attack by oxygen (O
275:
673:. Such species are important in glycochemistry, e.g., the
604:
connectivity. Deprotonation of organic carbonyls gives the
1040:, another form of ketones and aldehydes in water solutions
1095:
Clayden, Jonathan; Greeves, Nick; Warren, Stuart (2012).
65:, schematic representation of forms (see text regarding
786:
Keto–enol tautomerism is important in several areas of
811:to the enol phosphate ester. Metabolism of PEP to
1255:
1297:(6th ed.), New York: Wiley-Interscience,
632:(2,4-pentanedione), the enol form is favored.
1381:Ullmann's Encyclopedia of Chemical Technology
125:, enol-form at left, "keto" at right; Ex. is
8:
1447:. Oxford University Press. pp. 456–459.
935:The terminus of the double bond in enols is
675:Lobry de Bruyn-van Ekenstein transformation
99:, enol-form at left, keto at right. Ex. is
43:, keto-form at left, enol at right. Ex. is
1529:Enols and enolates in biological reactions
1254:Berg, Jeremy M.; Tymoczko, Stryer (2002).
1000:Diaryl-substitution stabilizes some enols.
1501:
1483:
793:The high phosphate-transfer potential of
1422:Journal of the American Chemical Society
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1221:Angewandte Chemie International Edition
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1055:
738:) in the (undesirable) process called
1158:Journal of Physical Organic Chemistry
7:
16:Organic compound with a C=C–OH group
1379:G. Roscher (2007). "Vinyl Esters".
1183:Schank, Kurt (1972). "Reductones".
943:organic compounds is important in
693:isomers at left and right. Ex. is
169:(R = many substituents). The term
14:
977:. Acylation gives esters such as
926:Carbonyl α-substitution reactions
888:
881:
851:
842:
833:
773:
114:
88:
54:
32:
825:substrate-level phosphorylation
640:Stereochemistry of ketonization
286:Selected enolization constants
687:Keto-enediol tautomerizations.
620:(K = / ≈ 3
203:. The keto and enol forms are
81:, also a less stabilized enol.
1:
1349:Mukaiyama, T.; Kobayashi, S.
807:catalyzes the dehydration of
749:Keto-enediol equilibrium for
1368:10.1002/0471264180.or046.01
949:synthetic organic chemistry
1590:
1443:Clayden, Jonathan (2012).
1262:(5th ed.). New York:
1070:(5th ed.). New York:
1068:Advanced Organic Chemistry
1066:Smith MB, March J (2001).
962:
923:
722:is a key substrate in the
931:Addition of electrophiles
913:
911:
887:
880:
850:
848:
841:
839:
832:
751:ribulose-1,5-bisphosphate
720:Ribulose-1,5-bisphosphate
596:Enols are derivatives of
271:illustrates this effect:
245:) from carbon to oxygen:
191:between a "keto" form (a
47:, a less stabilized enol.
1389:10.1002/14356007.a27_419
1264:W.H. Freeman and Company
1420:"Stable simple enols".
1383:. Weinheim: Wiley-VCH.
959:Deprotonation: enolates
689:Enediol in the center;
665:. One special case is
534:Hexafluoroacetylacetone
195:, named for the common
1554:Reactive intermediates
1317:Manfred Braun (2015).
1233:10.1002/anie.200502588
1074:. pp. 1218–1223.
1001:
939:. Its reactions with
821:adenosine triphosphate
809:2-phosphoglyceric acid
754:
716:
698:
570:Cyclohexa-2,4-dienone
497:Trifluoroacetylacetone
280:
173:is an abbreviation of
107:(---) stabilized enol.
23:Examples of keto-enol
1327:10.1002/9783527671069
999:
748:
706:
685:
608:, which are a strong
279:
237:bond adjacent to the
185:Keto–enol tautomerism
1197:10.1055/s-1972-21845
189:chemical equilibrium
63:resonance structures
1476:2013NatSR...3E1058Z
1430:10.1021/ja00203a019
1287:Smith, Michael B.;
1135:2011JChEd..88.1444M
795:phosphoenolpyruvate
287:
1564:Alkene derivatives
1464:Scientific Reports
1072:Wiley Interscience
1002:
755:
717:
699:
285:
281:
67:molecular orbitals
1574:Organic reactions
1544:Functional groups
1485:10.1038/srep01058
1445:Organic Chemistry
1304:978-0-471-72091-1
1164:(12): 1077–1083.
1143:10.1021/ed1010932
1129:(10): 1444–1445.
1106:978-0-19-927029-3
1097:Organic chemistry
917:
916:
697:, shown at right.
594:
593:
161:with the formula
159:organic chemistry
143:organic chemistry
77:at right; Ex. is
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1044:Regioselectivity
975:silyl enol ether
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740:photorespiration
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269:2,4-pentanedione
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151:Functional group
129:(reductone), an
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101:2,4-pentanedione
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819:(PK) generates
817:pyruvate kinase
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207:of each other.
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127:tartronaldehyde
123:tautomerization
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1523:External links
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1398:978-3527306732
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707:Conversion of
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695:hydroxyacetone
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558:C(O)CH=C(OH)CF
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484:C(O)CH=C(OH)CH
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374:Methyl acetate
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254:R′R′′ ⇌ RC(O
239:carbonyl group
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149:are a type of
133:-type of enol.
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982:
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979:vinyl acetate
976:
972:
966:
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956:
950:
946:
942:
941:electrophilic
938:
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709:ascorbic acid
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678:
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672:
668:
664:
656:
654:
652:
648:
647:diastereomers
639:
637:
633:
631:
630:acetylacetone
627:
626:1,3-diketones
619:
615:
614:vinyl alcohol
611:
607:
606:enolate anion
599:
598:vinyl alcohol
589:
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572:
569:
568:
564:
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532:
531:
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515:
498:
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460:Acetylacetone
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105:hydrogen bond
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1289:March, Jerry
1282:
1258:Biochemistry
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1184:
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1096:
1090:
1067:
1038:Geminal diol
1003:
992:
988:
985:Stable enols
968:
955:to an enol.
945:biochemistry
937:nucleophilic
934:
813:pyruvic acid
799:
792:
788:biochemistry
785:
782:Biochemistry
761:
724:Calvin cycle
718:
686:
660:
643:
634:
618:acetaldehyde
595:
415:Acetophenone
306:Acetaldehyde
266:
262:
214:
187:refers to a
184:
183:
179:portmanteaus
174:
170:
155:intermediate
146:
140:
1470:(1): 1058.
1352:Org. React.
947:as well as
651:enantiomers
610:nucleophile
299:enolization
211:Enolization
45:3-pentanone
25:tautomerism
1549:Metabolism
1538:Categories
1050:References
924:See also:
920:Reactivity
823:(ATP) via
767:resorcinol
671:reductones
628:, such as
398:=CH(OH)OCH
231:α-hydrogen
79:2-butanone
1494:2045-2322
1407:241676899
1205:260331550
1185:Synthesis
600:, with a
291:carbonyl
227:aldehydes
205:tautomers
201:electrons
121:Aldehyde
71:carbanion
1559:Alcohols
1512:23320139
1424:. 1989.
1291:(2007),
1241:16304647
1012:See also
971:enolates
713:vinylogy
667:catechol
663:acyloins
657:Enediols
624:10). In
443:C(OH)=CH
357:C(OH)=CH
258:)=CR′R′′
229:with an
193:carbonyl
61:Enolate
1503:3544012
1472:Bibcode
1131:Bibcode
1023:Enolase
1018:Alkenal
1006:phenols
965:enolate
805:enolase
763:Phenols
758:Phenols
691:acyloin
590:>10
337:Acetone
250:RC(=O)C
223:ketones
216:Organic
175:alkenol
131:enediol
95:Ketone
75:enolate
39:Ketone
1510:
1500:
1492:
1405:
1395:
1333:
1301:
1270:
1239:
1203:
1103:
1078:
1028:Ketone
802:enzyme
602:C=C−OH
574:Phenol
546:C(O)CF
542:C(O)CH
509:C(O)CF
505:C(O)CH
472:C(O)CH
468:C(O)CH
427:C(O)CH
345:C(O)CH
225:, and
219:esters
197:ketone
167:C=CROH
1569:Enols
1403:S2CID
1362:, 1.
1201:S2CID
491:0.27
323:=CHOH
294:enol
147:enols
1508:PMID
1490:ISSN
1393:ISBN
1356:1994
1331:ISBN
1299:ISBN
1268:ISBN
1237:PMID
1189:1972
1101:ISBN
1076:ISBN
1033:Ynol
800:The
616:and
565:~10
364:5.12
177:, a
171:enol
103:, a
1498:PMC
1480:doi
1426:doi
1385:doi
1364:doi
1323:doi
1229:doi
1193:doi
1166:doi
1139:doi
875:ATP
870:ADP
815:by
726:of
649:or
528:32
454:10
409:10
368:10
331:10
327:5.8
314:CHO
235:C−H
157:in
153:or
141:In
69:);
1540::
1506:.
1496:.
1488:.
1478:.
1466:.
1462:.
1401:.
1391:.
1360:46
1358:,
1329:.
1266:.
1235:.
1225:45
1223:.
1199:.
1187:.
1162:26
1160:.
1137:.
1127:88
1058:^
981:.
903:O
866:O
827:.
790:.
742:.
677:.
653:.
586:OH
554:CF
538:CF
517:CH
501:CH
480:CH
464:CH
394:CH
386:CH
382:CO
378:CH
353:CH
341:CH
319:CH
310:CH
221:,
145:,
1514:.
1482::
1474::
1468:3
1432:.
1428::
1409:.
1387::
1366::
1339:.
1325::
1276:.
1243:.
1231::
1207:.
1195::
1172:.
1168::
1145:.
1141::
1133::
1109:.
1084:.
953:2
901:2
899:H
864:2
862:H
753:.
736:2
715:.
622:×
584:5
582:H
580:6
578:C
560:3
556:3
548:3
544:2
540:3
523:3
519:3
511:3
507:2
503:3
486:3
482:3
474:3
470:2
466:3
452:×
450:1
445:2
441:5
439:H
437:6
435:C
429:3
425:5
423:H
421:6
419:C
407:×
405:4
400:3
396:2
388:3
384:2
380:3
366:×
359:2
355:3
347:3
343:3
329:×
321:2
312:3
297:K
256:H
252:H
243:H
233:(
165:2
163:R
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