18.6 base-catalyzed enolization: enolate anions
DESCRIPTION
18.6 Base-Catalyzed Enolization: Enolate Anions. ••. O. • •. R 2 C. CR'. H. Acidity of a -Hydrogen. ••. O. • •. –. R 2 C. CR'. + H +. ••. p K a = 16-20. ••. ••. O. O. • •. • •. –. R 2 C. R 2 C. CR'. CR'. ••. H. ••. –. O. • •. • •. R 2 C. CR'. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/1.jpg)
18.618.6
Base-Catalyzed Enolization:Base-Catalyzed Enolization:
Enolate AnionsEnolate Anions
![Page 2: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/2.jpg)
Acidity of Acidity of -Hydrogen-Hydrogen
+ + HH++RR22CC CR'CR'
OO•••• ••••
––
••••
OO••••
RR22CC CR'CR'
••••
HH
ppKKaa = 16-20 = 16-20
![Page 3: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/3.jpg)
Acidity of Acidity of -Hydrogen-Hydrogen
+ + HH++
RR22CC CR'CR'
OO••••
•••• ••••––
••••
RR22CC CR'CR'
OO ••••
––
••••
OO••••
RR22CC CR'CR'
••••
HH
ppKKaa = 16-20 = 16-20
![Page 4: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/4.jpg)
Acidity of Acidity of -Hydrogen-Hydrogen
OO••••
RR22CC CR'CR'
••••
HH
ppKKaa = 16-20 = 16-20
enolate ionenolate ion
+ + HH++
••••
RR22CC CR'CR'
OO•••• ••••––
RR22CC CR'CR'
OO•••• ••••
––
••••
![Page 5: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/5.jpg)
Mechanism of EnolizationMechanism of Enolization(Base-catalyzed)(Base-catalyzed)
OO••••
RR22CC CR'CR'
HH
OO
HH
•••••••••••• ––
••••
![Page 6: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/6.jpg)
Mechanism of EnolizationMechanism of Enolization(Base-catalyzed)(Base-catalyzed)
HHOO
HH
••••••••
OO••••
RR22CC CR'CR'
––••••••••
![Page 7: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/7.jpg)
Mechanism of EnolizationMechanism of Enolization(Base-catalyzed)(Base-catalyzed)
OO
HH
HH ••••OO••••
RR22CC CR'CR'
––••••••••••••
![Page 8: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/8.jpg)
Mechanism of EnolizationMechanism of Enolization(Base-catalyzed)(Base-catalyzed)
OO
HH
HH ••••
OO••••
RR22CC CR'CR'
––••••••••••••
![Page 9: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/9.jpg)
Mechanism of EnolizationMechanism of Enolization(Base-catalyzed)(Base-catalyzed)
HHOO••••
RR22CC CR'CR'
•••• OO
HH
••••––••••
••••
![Page 10: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/10.jpg)
Acidity of Acidity of -Hydrogen-Hydrogen
ppKKaa = 15.5 = 15.5 ppKKaa = 15.8 = 15.8
(CH(CH33))22CCHHCHCH
OO CCCCHH33
OO
![Page 11: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/11.jpg)
-Diketones are much more acidic-Diketones are much more acidic
CHCH33CCCCHH22CCHCCH33
OO OO
ppKKaa = 9 = 9
![Page 12: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/12.jpg)
HH33CCCC
CHCH33
OO
CCCC
OO
HH HH
HH33CCCC
CHCH33
OO
CCCC
OO
HH
HH++++••••––
-Diketones are much more acidic-Diketones are much more acidic
KKaa = 10 = 10–9–9
![Page 13: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/13.jpg)
HH33CCCC
CHCH33
OO
CCCC
OO
HH
••••––
-Diketones are much more acidic-Diketones are much more acidic
enolate of enolate of -diketone is stabilized; negative -diketone is stabilized; negative charge is shared by both oxygenscharge is shared by both oxygens
![Page 14: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/14.jpg)
-Diketones are much more acidic-Diketones are much more acidic
HH33CCCC
CHCH33
OO
CCCC
OO
HH
••••––
•••• ••••••••••••
HH33CCCC
CHCH33
OO
CCCC
OO
HH
–– •••• •••••••••••• ••••
![Page 15: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/15.jpg)
-Diketones are much more acidic-Diketones are much more acidic
HH33CCCC
CHCH33
OO
CCCC
OO
HH
••••––
•••• ••••••••••••
HH33CC
––
HH
CCCHCH33
OO
CCCC
OO•••• ••••
•••••••• ••••
![Page 16: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/16.jpg)
18.718.7
The Haloform ReactionThe Haloform Reaction
![Page 17: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/17.jpg)
Under basic conditions, halogenation of a Under basic conditions, halogenation of a methyl ketone often leads to carbon-carbon methyl ketone often leads to carbon-carbon bond cleavage.bond cleavage.
Such cleavage is called the haloform reaction Such cleavage is called the haloform reaction because chloroform, bromoform, or iodoform because chloroform, bromoform, or iodoform is one of the products.is one of the products.
The Haloform ReactionThe Haloform Reaction
![Page 18: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/18.jpg)
ExampleExample
(CH(CH33))33CCCCCCHH33
OO
BrBr22, NaOH, H, NaOH, H22OO
CCHBrHBr33++(CH(CH33))33CCONaCCONa
OO
(CH(CH33))33CCOHCCOH
OO
HH++
(71-74%)(71-74%)
![Page 19: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/19.jpg)
The haloform reaction is sometimes used as a The haloform reaction is sometimes used as a method for preparing carboxylic acids, but method for preparing carboxylic acids, but works well only when a single enolate can works well only when a single enolate can form.form.
The Haloform ReactionThe Haloform Reaction
ArCArCCHCH33
OO
(CH(CH33))33CCCCCHCH33
OO
RRCHCH22CCCHCH33
OO
yesyes yesyes nono
![Page 20: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/20.jpg)
RCCHRCCH33
OO
XX22, HO, HO––
RCCHRCCH22XX
OOXX22, HO, HO––
RCCHRCCHXX22
OO
XX22, HO, HO––
RCCRCCXX33
OO
MechanismMechanism
First stage is substitution of all available First stage is substitution of all available hydrogens by halogenhydrogens by halogen
![Page 21: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/21.jpg)
MechanismMechanism
Formation of the trihalomethyl ketone is Formation of the trihalomethyl ketone is followed by its hydroxide-induced cleavagefollowed by its hydroxide-induced cleavage
HOHO •••• ––••••
••••
•••• ––
RCRC
OO ••••
HOHO ••••••••
••••
CCXX33RCRC
OO ••••••••
CCXX33
––•••• CCXX33
••••
RCRC
OO ••••
OHOH••••
••••
++
++––•••• HCHCXX33
••••
RCRC
OO ••••
OO••••
••••++
![Page 22: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/22.jpg)
18.818.8
Some Chemical and StereochemicalSome Chemical and Stereochemical
Consequences of EnolizationConsequences of Enolization
![Page 23: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/23.jpg)
Hydrogen-Deuterium ExchangeHydrogen-Deuterium Exchange OO
HH
HH HH
HH++ 44DD22OO OO
DD
DD DD
DD++ 44DDOHOH
KOKODD, heat, heat
![Page 24: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/24.jpg)
MechanismMechanism
OODD••••––
••••
••••++
HOHODD
••••
••••++HH
OO
HH
HH
••••––•••• ••••
OO
HH
HH
HH
••••••••
HH
![Page 25: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/25.jpg)
MechanismMechanism
HH
OO
HH
HH
••••––•••• ••••
![Page 26: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/26.jpg)
MechanismMechanism
OODD••••––
••••
••••++
HH
OO
HH
HH
••••––•••• ••••
OO
HH
HH
DD
••••••••
HH
OODD••••
••••DD
![Page 27: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/27.jpg)
Stereochemical Consequences of EnolizationStereochemical Consequences of Enolization CC CCCC66HH55
OOHH
CHCH33CHCH22
HH33CC
100% R100% R
HH33OO++
HH22O, HOO, HO––
50% R50% S
50% R50% S
50% R50% S
50% R50% S
![Page 28: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/28.jpg)
Enol is achiralEnol is achiral CC CCCC66HH55
OOHH
CHCH33CHCH22
HH33CC
RR
CCCC66HH55
OHOH
CC
HH33CC
CHCH33CHCH22
![Page 29: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/29.jpg)
Enol is achiralEnol is achiral CC CCCC66HH55
OOHH
CHCH33CHCH22
HH33CC
RR
CCCC66HH55
OHOH
CC
HH33CC
CHCH33CHCH22
CC CCCC66HH55
OOHH
CHCH33CHCH22
HH33CC
SS50%50%
50%50%
![Page 30: 18.6 Base-Catalyzed Enolization: Enolate Anions](https://reader035.vdocument.in/reader035/viewer/2022081507/56815971550346895dc6b4bb/html5/thumbnails/30.jpg)
Results of Rate StudiesResults of Rate Studies CC CCCC66HH55
OOHH
CHCH33CHCH22
HH33CC
Equal rates for:Equal rates for:racemizationracemizationH-D exchangeH-D exchangebrominationbrominationiodinationiodination
Enol is intermediate Enol is intermediate and its formation is and its formation is rate-determiningrate-determining