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Chapter 14 Aldehydes, Ketones, and Chiral Molecules 14.1 Aldehydes and Ketones Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Carbonyl Group in Aldehydes and Ketones A carbonyl group • In an aldehyde is attached to at least one H atom. • In a ketone is attached to two carbon groups. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Naming Aldehydes An aldehyde • Has an IUPAC name in which the -e in the alkane name is changed to -al. • Has a common name for the first four aldehydes that use the prefixes form- (1C), acet- (2C), propion- (3C), and butyr(4C), followed by aldehyde. O O O ║ ║ ║ H−C−H CH3−C−H CH3−CH2−C−H methanal ethanal propanal (formaldehyde) (acetaldehyde) (propionaldehyde) Naming Aldehydes Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Aldehydes in Flavorings • Several naturally occurring aldehydes are used as flavorings for foods and fragrances. O H C Benzaldehyde (almonds) O CH=CH C H Cinnamaldehyde (cinnamon) Naming Ketones Ketones are named • In the IUPAC system by replacing the -e in the alkane name with -one. The carbonyl carbon is indicated by a number. • With a common name by indicating the alkyl groups attached to the carbonyl group in alphabetical order followed by ketone. O O ║ ║ CH3−C−CH3 CH3−C−CH2−CH3 propanone 2-butanone (dimethyl ketone) (ethyl methyl ketone) Ketones in Common Use Butter flavoring Nail polish remover, Solvent Propanone, Dimethylketone, Acetone Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Learning Check Classify each as 1) aldehyde or 2) ketone. O O || || A. CH3—CH2—C—CH3 B. CH3—C—H CH3 O | || C. CH3—C—CH2—C—H | CH3 O D. Solution A. 2) ketone B. 1) aldehyde C. 1) aldehyde D. 2) ketone Learning Check Classify each as an aldehyde (1), ketone (2), alcohol (3), or ether (4). O ║ A. CH3─CH2─C─CH3 B. CH3─O─CH3 CH3 O │ ║ C. CH3─C─CH2─C─H │ CH3 OH │ D. CH3─CH─CH3 Solution Classify each as an aldehyde (1), ketone (2), alcohol (3), or ether (4). O ║ A. CH3─CH2─C─CH3 B. CH3─O─CH3 (2) ketone (4) ether CH3 O OH │ ║ │ C. CH3─C─CH2─C─H D. CH3─CH─CH3 │ CH3 (1) aldehyde (3) alcohol Learning Check Name each of the following: O ║ 1. CH3─CH2─CH2─CH2─C─H O ║ 2. Cl─CH2─CH2─C─H O ║ 3. CH3─CH2─C─CH3 Solution O ║ 1. CH3─CH2─CH2─CH2─C─H pentanal O ║ 2. Cl─CH2─CH2─C─H 3-chloropropanal O ║ 3. CH3─CH2─C─CH3 2-butanone; ethyl methyl ketone Learning Check Name the following compounds. O || A. CH3—CH2—CH2—C—CH3 B. O CH3 O | || C. CH3—C—CH2—C—H | CH3 Solution A. 2-pentanone; methyl propyl ketone B. cyclohexanone C, 3,3-dimethylbutanal Chapter 14 Aldehydes, Ketones, and Chiral Molecules 14.2 Physical Properties Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Polar Carbonyl Group The polar carbonyl group • Provides dipole-dipole interactions. δ+ δδ+ δC=O C=O • Does not have H on the oxygen atom. • Cannot form hydrogen bonds. Boiling Points Aldehydes and ketones have • Polar carbonyl groups (C=O). δ+ δC=O • Attractions between polar groups. δ+ δδ+ δC=O C=O • Higher boiling points than alkanes and ethers of similar mass. • Lower boiling points than alcohols of similar mass. Comparison of Boiling Points 58 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Learning Check Select the compound in each pair that would have the Higher boiling point. A. CH3—CH2—CH3 or CH3—CH2—OH O B. or C. CH3—CH2—OH or CH3—O—CH3 Solution A. CH3—CH2—OH O B. C. CH3—CH2—OH Solubility in Water The electronegative O atom of the carbonyl group in aldehydes and ketones forms hydrogen bonds with water. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 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 Solution A. CH3—CH2—CH3 insoluble B. CH3—CH2—OH soluble O || C. CH3—CH2—CH2—C—H soluble O || D. CH3—C—CH3 soluble Chapter 14 Aldehydes, Ketones and Chiral Molecules Oxidation and Reduction Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Oxidation • Aldehydes are easily oxidized to carboxylic acids. O O || [O] || CH3—C—H CH3—C—OH Acetaldehyde Acetic acid 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. ERROR: stackunderflow OFFENDING COMMAND: ~ STACK: