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Terminology

O. CH 3 CH 2 CH 2 CH. Terminology. The reference atom is the carbonyl carbon. Other carbons are designated a , b , g , etc. on the basis of their position with respect to the carbonyl carbon. Hydrogens take the same Greek letter as the carbon to which they are attached. g. b. a. H.

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Terminology

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  1. O CH3CH2CH2CH Terminology • The reference atom is the carbonyl carbon. • Other carbons are designated a, b, g, etc. on the basis of their position with respect to the carbonyl carbon. • Hydrogens take the same Greek letter as the carbon to which they are attached. g b a

  2. H •• O H O •• •• •• R2C CR' H O H •• •• H Mechanism of Enolization(In general)

  3. •• O •• R2C CR' H •• O H •• R2C CR' Mechanism of Enolization(In general)

  4. H •• O H O •• •• + H R2C CR' H Mechanism of Enolization(Acid-catalyzed)

  5. Mechanism of Enolization(Acid-catalyzed) H + •• H O O •• •• H R2C CR' H

  6. Mechanism of Enolization(Acid-catalyzed) + •• H O R2C CR' H

  7. H O •• •• H Mechanism of Enolization(Acid-catalyzed) + •• H O R2C CR' H

  8. •• H O •• R2C CR' H + O H •• H Mechanism of Enolization(Acid-catalyzed)

  9. OH O R2CHCR' R2C CR' Enol Content • percent enol is usually very small • keto form usually 45-60 kJ/mol more stablethan enol keto enol

  10. OH O CH3CH H2C CH OH O CH3CCH3 H2C CCH3 Enol Content K = 3 x 10-7 K = 6 x 10-9

  11. 18.5 Stabilized Enols

  12. O OH H H H H H H H H H H H 2,4-Cyclohexadienone • keto form is less stable than enol form • keto form is not aromatic • enol form is aromatic

  13. O OH O O CH3C CH3CCH2CCH3 CHCCH3 1,3-Diketones(also called b-diketones) Example: 2,4-pentanedione • keto form is less stable than enol form (20%) (80%)

  14. Enol form of 2,4-pentanedione

  15. Enol form of 2,4-pentanedione intramolecular hydrogen bond 103 pm 166 pm H O O 133 pm 124 pm C C H3C C CH3 134 pm 141 pm H C=C and C=O are conjugated

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