XV. Carbonyls III, Enolates.pdf

XV. Carbonyls III, Enolates.pdf - XV Enols and Enolates...

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1 XV. Enols and Enolates Competitive Carbonyl Reactions Acidity of α− Hydrogens pK a > 60 Aldehydes and Ketones: delocalized enolate anion
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2 Ester: esters are less acidic than aldehydes and ketones because the oxygen lone pair is also delocalized onto the carbonyl Active Methylene Compounds:
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3 Keto-Enol Tautomerism enol form is stabilized by conjugation and intramolecular hydrogen bonding Base Catalyzed Enolization
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4 Acid Catalyzed Enolization Halogenation of the α -Carbon Acid Catalyzed: Mechanism The next halogen adds more slowly since: R C CH 3 O X 2 H + or HO - R C CH 2 X O is more stable than RCH C OH R RC C OH R Br
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5 Base Promoted: The next halogen adds faster since: Hell-Volhard-Zelinsky Reaction mechanism Replacing the a-Halogen is more stable than RC C O R Br RCH C O R
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6 Alkylation of the α -Carbon Forming an Enolate Ion Using LDA to Form an Enolate Direct alkylation:
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7 Alkylating Unsymmetrical Ketones kinetic product thermodynamic product (less steric hindrance) (more stable enolate) major –low temp major – high temp -bulky base -small base enolate formation irreversible
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  • Fall '17
  • Finzel
  • Carbonyl, ketone, Keto-enol tautomerism, Enol, Intramolecular condensations

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