Properties of Aldehydes and Ketones

1. Properties of Aldehydes and Ketones

2. Physical Properties • The polar carbonyl group provides dipole-dipole interactions. + -+ - C=O C=O • Without an H on the oxygen, aldehydes and ketones cannot form hydrogen bonds.

3. Boiling Points Aldehydes and ketones have • polar carbonyl groups (C=O). + - C=O • attractions between polar groups. + -+ - C=O C=O • higher boiling points than alkanes and ethers of similar mass. • lower boiling points than alcohols of similar mass.

4. Comparison of Boiling Points 58

5. Solubility in Water The electronegative O atom of the carbonyl group of aldehydes and ketones forms hydrogen bonds with water.

6. Learning Check Indicate if each is soluble or insoluble in water. A. CH3—CH2—CH3 B. CH3—CH2—OH O || C. CH3—CH2—CH2—C—H O || D. CH3—C—CH3

7. Solution Indicate if each is soluble or insoluble in water. A. CH3—CH2—CH3insoluble B. CH3—CH2—OH soluble O || C. CH3—CH2—CH2—C—H soluble O || D. CH3—C—CH3soluble

8. Tollens’ Test InTollens’ test, • Tollens’ reagent, which contains Ag+, oxidizes aldehydes, but not ketones. • Ag+ is reduced to metallic Ag, which appears as a “mirror” in the test tube.

9. Benedict’s Test In the Benedict’s test, • Benedict’s reagent, which contains Cu2+,reacts with aldehydes that have an adjacent OH group. • An aldehyde is oxidized to a carboxylic acid, while Cu2+ is reduced to give red Cu2O(s).

10. Learning Check Write the structure and name of the oxidized product when each is mixed with Tollens’ reagent. A. butanal B. acetaldehyde C. ethyl methyl ketone

11. Solution A. butanal O || CH3—CH2—CH2—C—OH butanoic acid B. acetaldehyde O || CH3—C—OH acetic acid C. ethyl methyl ketone None. Ketones are not oxidized by Tollen’s reagent.