Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Chapter 12 Organic Compounds with Oxygen and Sulfur 12.5 Properties of Aldehydes and Ketones 1 In Tollens’ test, a silver mirror forms when the oxidation of an aldehyde reduces silver ion to metallic silver. The silvery surface of a mirror is formed in a similar way.

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Physical Properties The polar carbonyl group provides dipole-dipole interactions.  +  -  +  - C=O Because the electronegative oxygen atom forms hydrogen bonds with water molecules, aldehydes and ketones with one to four carbons are very soluble. 2

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solubility of Aldehydes and Ketones in Water 3

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solubility in Water The electronegative O atom of the carbonyl group of aldehydes and ketones forms hydrogen bonds with water. 4

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check Indicate whether each is soluble or insoluble in water. A. CH 3 —CH 2 —CH 3 B. CH 3 —CH 2 —OH O || C. CH 3 —CH 2 —CH 2 —C—H O || D. CH 3 —C—CH 3 5

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution Indicate whether each is soluble or insoluble in water. A. CH 3 —CH 2 —CH 3 insoluble B. CH 3 —CH 2 —OH soluble O || C. CH 3 —CH 2 —CH 2 —C—H soluble O || D. CH 3 —C—CH 3 soluble 6

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Oxidation of Aldehydes Primary alcohols can be oxidized to aldehydes, which can be easily oxidized to carboxylic acids. Secondary alcohols can be oxidized to ketones, which cannot be further oxidized. 7

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Tollens’ Test In Tollens’ 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. 8

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Tollens’ Test 9

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Benedict’s Test In Benedict’s test, Benedict’s reagent, which contains Cu 2+, reacts with aldehydes that have an adjacent OH group. 10

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Benedict’s Test In Benedict’s test, an aldehyde is oxidized to a carboxylic acid, while Cu 2+ is reduced to give red Cu 2 O(s). 11 The blue Cu 2+ in Benedict’s solution forms a brick-red solid of Cu 2 O in a positive test for many sugars and aldehydes with adjacent hydroxyl groups.

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Reduction of Aldehydes and Ketones Aldehydes and ketones can be reduced by sodium borohydride, NaBH 4, or H 2. The reduction of aldehydes and ketones decreases the number of carbon–oxygen bonds by addition of hydrogen or loss of oxygen. 12

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check Write the structure and name of the organic product when each is mixed with Tollens’ reagent. A. butanal B. acetaldehyde C. ethyl methyl ketone 13

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution A. O O || Tollens’ || CH 3 —CH 2 —CH 2 —C—OH butanal butanoic acid B. O O || Tollens’ || CH 3 —C—H CH 3 —C—OH acetaldehyde acetic acid C. Ethyl methyl ketone + Tollens’ No reaction Ketones are not oxidized by Tollens’ reagent. 14