24. Enolate Chemistry: Reactions at the Alpha-Carbon

For each molecule shown below,

1. indicate the most acidic hydrogens.

2. draw the important resonance contributors of the anion that results from removal of the most acidic hydrogen.

(h)

For each molecule shown below,

1. indicate the most acidic hydrogens.

2. draw the important resonance contributors of the anion that results from removal of the most acidic hydrogen.

(e)

Draw the products of the following reactions:

a.

Give the important resonance forms for the possible enolate ions of the following:

(d)

Give the important resonance forms for the possible enolate ions of the following:

(e)

Show the resonance forms for the enolate ions that result when the following compounds are treated with a strong base.

(a) ethyl acetoacetate

(b) pentane-2,4-dione

2. Indicate which compounds would be more than 99% deprotonated by a solution of sodium ethoxide in ethanol.

Give the important resonance forms for the possible enolate ions of the following:

(f)

LDA can be used to form enolates on esters and nitriles. Predict the product of these alkylation reactions.

(a)

In Chapter 20, we studied the aldol reaction. Although not discussed at the time, this reaction is stereospecific, proceeding through the Zimmerman–Traxler transition state shown here.

(a) Show an arrow-pushing mechanism for this concerted reaction.

(b) Why is this a favorable mechanism?

Give the important resonance forms for the possible enolate ions of the following:

(a) acetone

(b) cyclopentanone

Draw the products of the following reactions:

b.

For each molecule shown below,

2. draw the important resonance contributors of the anion that results from removal of the most acidic hydrogen.

(a)

(b)

(c)

For each molecule shown below,

1. indicate the most acidic hydrogens.

(a)

(b)

(c)

When cis-2,4-dimethylcyclohexanone is dissolved in aqueous ethanol containing a trace of NaOH, a mixture of cis and trans isomers results. Propose a mechanism for this isomerization.