25. Condensation Chemistry

Which major product is formed when $\mathrm{benzaldehyde}$ reacts with $\mathrm{acetone}$ in the presence of $\mathrm{sodium} \mathrm{hydroxide}$ in an $\mathrm{aldol} \mathrm{condensation}$ reaction?

Which of the following is the major enone product formed from the aldol self-condensation of ${\mathrm{CH}}_3\mathrm{COCH}{2}_2\mathrm{CH}{3}_3$ (3-pentanone) under basic conditions, followed by dehydration?

The following compounds can be synthesized by aldol condensations, followed by further reactions. (In each case, work backward from the target molecule to an aldol product, and show what compounds are needed for the condensation.)

(b)

Which statement best explains why $\mathrm{aldol}$ reactions involving $\mathrm{ketones}$ typically give low yields?

Show how the following compounds can be synthesized. The only carbon-containing compounds available to you for each synthesis are shown.

b.

Predict the products of the following aldol condensations. Show the products both before and after dehydration.

(a)

Predict the products of aldol condensation, followed by dehydration, of the following ketones and aldehydes.

(b) acetophenone

Propose a complete mechanism for the acid-catalyzed aldol condensation of acetone.

The Knoevenagel condensation is a special case of the aldol condensation in which an active methylene compound reacts with an aldehyde or ketone, in the presence of a secondary amine as a basic catalyst, to produce a new C=C. Show the starting materials that made each of these by a Knoevenagel condensation.

(c)

Give the expected products for the aldol condensations of (a) propanal.

Biochemists studying the structure of collagen (a fibrous protein in connective tissue) found cross-links containing α,β-unsaturated aldehydes between protein chains. Show the structures of the side chains that react to form these cross-links, and propose a mechanism for their formation in a weakly acidic solution.

Predict the products of aldol condensation, followed by dehydration, of the following ketones and aldehydes.

(c) cyclohexanone

What aldol addition product is formed from each of the following compounds?

b.

Propose mechanisms for the reactions shown in Problems 22-63 part (a).

An aldol addition can be catalyzed by acids as well as by bases. Propose a mechanism for the acid-catalyzed aldol addition of propanal.