Q23-5P - Organic Chemistry (Mcmurry)

Question

Which of the following compounds are aldol condensation products? What is the aldehyde or ketone precursor of each?

(a) 2-Hydroxy-2-methylpentanal      (b) 5-Ethyl-4-methyl-4-hepten-3-one

Step-by-Step Solution

Answer

aldol condensation products must contain β – hydroxyl group to the carbonyl group and are called β – hydroxyl aldehyde or ketones.

a. No, 2-Hydroxy-2-methylpentanal does not a product of aldol condensation.

b. Yes,5-Ethyl-4-methyl-4-heptane-3-one is an aldol condensation product and the compound is formed when 3-pentanone undergoes an aldol self-condensation reaction and after that dehydration occurs:

Step 1: Structure of 2-Hydroxy-2-methylpentanal:

From the structure, it is clear that this compound does not have a β – hydroxyl group in its structure.

Hence, this compound does not a product of aldol condensation

$$\begin{gathered} \overline{)\mathrm{OH}} \mathrm{O} \\ | || \\ {\mathrm{CH}}_3-{\mathrm{CH}}_2-{\mathrm{CH}}_2-\mathrm{C}-\mathrm{CH} \\ | \\ {\mathrm{CH}}_3 \end{gathered}$$

Step 2: Structure of 5-Ethyl-4-methyl-4-hepten-3-one :

This compound is formed when 3-pentanone undergoes an aldol self-condensation reaction and after that dehydration occurs:

$$\begin{gathered} {\mathrm{H}}_3\mathrm{C} \mathrm{O} \\ | || \\ {\mathrm{CH}}_3-{\mathrm{CH}}_2-\mathrm{C}=\mathrm{C}-\mathrm{C}-{\mathrm{CH}}_2{\mathrm{CH}}_3 \\ | \\ {\mathrm{CH}}_2-{\mathrm{CH}}_3 \end{gathered}$$