24. Enolate Chemistry: Reactions at the Alpha-Carbon

Propose a mechanism for each of the following reactions:

a.

Which of the following represents the most favored enol tautomer of ${\mathrm{CH}}_3\mathrm{COCH}{3}_{}$ (acetone)?

Which of the following structures represents the enol form that is a tautomer of the aldehyde ${\mathrm{CH}}_3\mathrm{CHO}$ (acetaldehyde)?

Which of the following represents the enol form of ${\mathrm{CH}}_3\mathrm{COCH}{3}_{}$ (acetone)?

Which of the following best describes what happens when a tautomeric shift occurs?

Draw the enol tautomer for cyclopentanone

Cytosine, uracil, and guanine have tautomeric forms with aromatic hydroxy groups. Draw these tautomeric forms.

Draw the enol tautomers for each of the following compounds. For compounds that have more than one enol tautomer, indicate the one that is more stable.

f.

Which of the following best represents the enol tautomer of ${\mathrm{CH}}_3{\mathrm{CO}}_2\mathrm{CH}{3}_2$ (acetone)?

Vinyl alcohols are generally unstable, quickly isomerizing to carbonyl compounds. Propose mechanisms for the following isomerizations.

(a)

Show each step in the mechanism of the acid-catalyzed interconversion of (R)- and (S)-3-methylpentan-2-one.

Phenylacetone can form two different enols.

(c) Propose mechanisms for the formation of the first enol in base.

A β-ɣ-unsaturated carbonyl compound rearranges to a more stable conjugated ⍺,β-unsaturated compound in the presence of either acid or base. b. Propose a mechanism for the acid-catalyzed rearrangement.