Enols%20and%20Enolates

Enols%20and%20Enolates - Enols and Enolates O C C H O C H C...

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Enols and Enolates 2 C O C H C O H C keto form enol form keto-enol tautomerization base C O C C O C enolate ion - resonance stabilized carbanion 3 I. α -Halogenation of Aldehydes and Ketones C O C H C OH C C C C C O α β γ . . . X 2 C O C X + HX X X C O C X H + X
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4 I. α -Halogenation of Aldehydes and Ketones (cont.) O Cl 2 O Cl O O Br Br 2 α -chloroacetone (strong lachrymator!) 5 A. Keto-enol tautomerization C O C H C O H C K eq ~ 10 -7 - 10 -9 acid-catalyzed: base-catalyzed: C O C H C O C H C O H C C O H C C O C H H C O C H H C O C C O C H + -H + OH - H 2 O + OH -
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6 B. Stabilized enols O OH K ~ O O O O H 1,3-diketones ( β -diketones): K ~ 4 conjugation H-bonding 7 C. Enolate ions + H 2 O + OH - C O C H K a ~ 10 -16 K a ~ 10 -16 K eq ~ 1 K a ~ 10 -16 C O C H + + C O C C O C N C O C N H K a ~ 10 -40 Li Li K eq ~ 10 24 lithium diisopropylamide (LDA) resonance stabilized
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8 A. Haloform reaction R C O CH 3 R C O O + CH X 3 X 2 OH - methyl ketone haloform R C O CH 3 + 3X 2 + 4OH - RCO 2 - + CH X 3 + 3X - + 3H 2 O iodoform test for methyl ketones: iodoform (voluminous yellow precipitate) I 2 OH - + CH I 3 R C O O R C O CH 3 9 A. Haloform reaction (cont.) R C O CH 3 R C O CH 2 X R C O CHX 2 X 2 OH - X 2 OH - X 2 OH - R C O CX 3 HO - R C O OH CX 3 R C O OH + CX 3 RCO 2 - + HCX 3 + H 2 O + X - + H 2 O + X - R C O CX 3 + H 2 O + X -
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10 1. aldehydes
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Enols%20and%20Enolates - Enols and Enolates O C C H O C H C...

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