Ch 18

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mckenzielarmstrong
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192677
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Ch 18
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2013-01-13 21:21:59
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Reactions α Carbon Carbonyl Compounds Enols Enolates
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Ch 18
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  1. The carbon atom adjacent to a carbonyl group
    a Carbon
  2. The hydrogen atom on an α carbon; this H is unusually acidic, with a pKa between 17 and 20 for most monocarbonyl compounds, or a pKa between 9 and 11 for most β-dicarbonyl compounds. Also called α proton
    a Hydrogen
  3.  An alkene alcohol that is formed by tautomerization of an aldehyde or ketone, which has the general formula: R2C=C(OH)R'
    Enol
  4. An α-hydrogen that is lost and regained through keto-enol tautomerization, thus losing its stereochemistry in the process
    Enolizable hydrogen
  5. The resonance-stabilized anion formed by deprotonating the α carbon atom adjacent to a carbonyl group, or by deprotonating the hydroxyl group of an enol tautomer.
    Enolate anion
  6. Constitutional isomers that are easily interconverted; keto and enol tautomers differ in the position of a hydrogen atom and are rapidly interconverted in the presence of an acid or base
    Tautomers
  7. Process by which two isomers are interconverted by the movement of an atom or a group (usually a hydrogen atom); in the presence of an acid or base, keto and enol tautomers are in equilibrium: RCH2COR' ↔ RCH=C(OH)R'
    Tautomerization
  8. Compounds that have two carbonyl groups, >C=O, that are separated by one carbon atom, with the general formula, RCOCH2COR
    β-Dicarbonyl
  9. Replacement of a hydrogen atom on the α carbon atom of a carbonyl compound by some other group
    Alpha substitution
  10. Diastereomers that differ in configuration at only one chirality (stereogenic) center
    Epimers
  11. Conversion of a less stable epimer to a more stable epimer by keto-enol tautomerization.
    Epimerization
  12. Compound formed by replacing three hydrogen atoms in methane, CH4 , with halogen atoms to form CHX3
    Haloform
  13. The reaction of a methyl ketone with a halogen and base to produce a carboxylate ion, RCOO‾, and a haloform, CHX3
    Haloform rxn
  14.  A chemical test for methyl ketones, which react with iodine, I2 , and base (usually aqueous NaOH) to produce a precipitate of iodoform, CHI3 , which is a yellow solid.
    Iodoform test
  15. Alpha-Halogenation of a carboxylic acid in the presence of catalytic phosphorus, to give an α-halo carboxylic acid; the reaction initially forms an acyl halide, which is in equilibrium with the enol form that undergoes alpha substitution with the halide, then the α-halo acyl halide is hydrolyzed with water to the α-halo carboxylic acid.
    Hell–Volhard–Zelinski Reaction
  16. The most stable enolate formed from an unsymmetrical ketone, which has the more highly substituted double bond; it is favored by use of a protic solvent with a base that is weaker than the enolate ion, such as hydroxide ion or alkoxide ion, so that equilibrium can be established
    Thermodynamic enolate
  17. The enolate formed fastest from an unsymmetrical ketone, which usually has the least substituted double bond; it is favored by use of a very strong, sterically hindered base, such as LDA (lithium diisopropylamide), in an aprotic solvent that is unreactive with bases, such as an ether like THF (tetrahydrofuran) or DME (dimethoxyethane).
    Kinetic enolate
  18. A very strong, sterically hindered base, ( i-C3H7 )2 N‾ Li+ , whose conjugate acid has pKa = 38. Abbreviated LDA.
    Lithium diisopropylamide
  19. An alkylation reaction involving the conversion of a ketone into its enolate with LDA (lithium diisopropylamide), followed by an SN 2 reaction with a primary alkyl halide.
    Direct alkylation of ketones
  20.  An alkylation reaction involving the conversion of an ester into its enolate with LDA (lithium diisopropylamide), followed by an SN 2 reaction with a primary alkyl halide.
    Direct alkylation of esters
  21. A reaction whereby a β-keto carboxylic acid, or a β-dicarboxylic acid, loses a carboxyl group as carbon dioxide, CO2
    Decarboxylation of β-keto acids
  22. Base-catalyzed alkylation or arylation of the enolate of a β-ketoester to produce a monoalkyl or dialkyl acetoacetic ester; subsequent hydrolysis of the ester and decarboxylation produces a monosubstituted or disubstituted acetone (methyl ketone).
    Acetoacetic ester synthesis
  23. A reagent whose structure, when incorporated into a product, appears to have originated from one type of precursor, when as a reactant it actually had a different origin. For example, the ethyl acetoacetate enolate ion serves as the synthetic equivalent of the acetone enolate ion, and the diethyl malonate enolate ion serves as the synthetic equivalent of the ethyl acetate enolate ion
    Synthetic equivalent
  24. Synthesis based on the strongly activated methylene group of malonic esters, which easily deprotonate in base to form a resonance-stabilized anion that can be alkylated or acylated to produce a monoalkyl or dialkyl malonic ester; subsequent hydrolysis of the ester and decarboxylation produces a monosubstituted or disubstituted acetic acid.
    Malonic ester synthesis
  25. A compound that has two electron-withdrawing groups attached to the same methylene carbon atom, Z-CH2-Z' , which makes the methylene hydrogen atoms acidic, with a pKa between 3 and 13
    Active hydrogen compound
  26. A vinyl amine, usually generated by the acid-catalyzed reaction of a secondary amine with an aldehyde or ketone, which has the general formula: R2C=C(NR2)R.
    Enamine
  27. Synthesis of an α-alkyl or α-acyl carbonyl compound from the reaction of an enamine with an alkyl or acyl halide.
    Stork enamine reaction

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