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Chapter Fifteen Aldehydes And Ketones Aldehydes and Ketones In an aldehyde, an H atom is attached to a carbonyl group O carbonyl group CH3-C-H In a ketone, two carbon groups are attached to a carbonyl group O carbonyl group CH3-C-CH3 Chapter 15 | Slide 2 of 36 Chapter 15 | Slide 3 of 36 Ketones as Hormones Chapter 15 | Slide 4 of 36 Aldehydes and Ketones cont’d ← Fig. 15.1 Aldehydes and ketones are related to alcohols in the same manner that alkenes are related to alkanes. Chapter 15 | Slide 5 of 36 Aldehydes and Ketones → Fig. 15.3 Aldehydes and ketones with the same number of carbon atoms and the same degree of saturation are structural isomers. Chapter 15 | Slide 6 of 36 Naming Aldehydes • • • • Aldehydes are named by replacing the “e” with “____.” The parent chain must contain the –_______ group. The –CHO carbon is always carbon ___. When attached to a ring “carbaldehyde” is used. O O 3 5 O propaneal 6 4 2 1 4-ethyl 2,5-dimethyl 2- hexen eal cyclopentanecarbaldehyde Chapter 15 | Slide 7 of 36 Aldehydes and Ketones cont’d ← Fig. 15.2 Benzaldehyde, the simplest aromatic aldehyde. . Chapter 15 | Slide 8 of 36 Naming Ketones • Ketones are named by replacing the “e” with “_____.” • The parent chain must contain the ______. • Numbering begins nearer the ______. O 7 O 6 5 4 3 2 1 5-ethyl 3,6-dimethyl 2- heptan eone 2- butan eone Chapter 15 | Slide 9 of 36 Name these aldehydes/ketones. O O 3-penten-2-one 5-methyl-3-cyclohexenone O O 2-phenylpropanal cyclohexanone Chapter 15 | Slide 10 of 36 Aldehydes and Ketones cont’d ←C.C 15.1 ←Wood Smoke contains formaldehyde and causes eyes to tear. ←Formaldehyde is a lachrymator (eye irritant) © Harvey Lloyd/Peter Arnold, Inc. Chapter 15 | Slide 11 of 36 Aldehydes and Ketones cont’d ← Fig. 15.4 Formalin is used to preserve biological specimens. © 2005 Norbert Wu / www.norbertwu.com Chapter 15 | Slide 12 of 36 Aldehydes and Ketones → Fig. 15.5 The delightful odor of melted butter is largely due to butanedione. © Steven Needham / Envision Chapter 15 | Slide 13 of 36 Aldehydes and Ketones cont’d Chapter 15 | Slide 14 of 36 Aldehydes and Ketones Why are some aldehydes and ketones soluble in water? Chapter 15 | Slide 15 of 36 Physical Properties of Aldehydes and Ketones • The polarity of the carbonyl group in aldehydes and ketones, which is responsible for many of their physical properties. – They have boiling points _______ than alcohols but _______ than alkanes. • Why? – Nonpolar < Polar (Dipole-dipole) <H-bonds – _____ molecular weight aldehydes and ketones are __________ in water • Why not ________ molecular weight aldehydes and ketones? – Most aldehydes and ketones have odors Chapter 15 | Slide 16 of 36 Aldehydes and Ketones Chapter 15 | Slide 17 of 36 Synthesis of Aldehydes and Ketones O • Oxidation of alcohols. – Primary alcohols yield aldehydes. – Secondary alcohols yield ketones. From primary alcohols O From secondary alcohols Chapter 15 | Slide 18 of 36 • Oxidation reactions: OH PCC CH2Cl2 R PCC = Pyridinium chlorochromate OH Na2Cr2O7, H2O, CH3CO2H R R Chapter 15 | Slide 19 of 36 Oxidation of Aldehydes • Ketones are unreactive to oxidation because no hydrogens are on the carbon. O O R H AgNO3 NH4OH R OH O AgNO3 NH4OH R No Reaction R' Chapter 15 | Slide 20 of 36 Reduction of Aldehydes and Ketones • Reduction: Adding hydrogen across the carbonyl – Aldehyde primary alcohol – Ketone secondary alcohol CH CH2 O + H2 H3C H3C O OH + H2 C H3C OH CH3 CH H3C CH3 Chapter 15 | Slide 21 of 36 Addition Reactions • Polar molecules can add to the carbonyl in aldehydes and ketones • The negative part of the added molecule adds to the positive carbonyl carbon • The positive part of the added molecule adds to the negative carbonyl oxygen • d+ d- d+ d• -C=O + X-Y -C-O-X Y Chapter 15 | Slide 22 of 36 Acetal Formation • Alcohols add to the carbonyl of aldehydes and ketones • The addition of two alcohols forms an acetal. • O O-CH3 • CH3-C-H + 2 CH3-OH CH3-C-H + H2O • O-CH3 Hydrolysis of acetals yield the aldehyde or ketone and the alcohols that originally formed the acetal Chapter 15 | Slide 23 of 36 Hemiacetal Formation • The addition of one alcohol to an aldehyde or ketone forms an intermediate called a hemiacetal • Usually, hemiacetals are unstable and hard to isolate. • O O-CH3 • CH3-C-H + 2 CH3-OH CH3-C-H + H2O • O-H Chapter 15 | Slide 24 of 36 Aldehydes and Ketones CC 15.3 Diabetes, aldehyde oxidation, and glucose testing Chapter 15 | Slide 25 of 36 Tests for Distinguishing between Aldehydes and Ketones • Tollens’ test (AKA Silver Mirror test) – Tollens’ reagent, which contains Ag+, reacts with aldehydes, but not with ketones – The aldehyde is oxidized and Ag+ is reduced to Ag, which appears as a silver “mirror” in the test tube (or reaction vessel) Chapter 15 | Slide 26 of 36 Aldehydes and Ketones cont’d Figs. 15.8 a-c (a) An aqueous solution of ethanal is added to a solution of silver nitrate. (b) The solution darkens as ethanal is oxidized to ethanoic acid. (c) The inside of the beaker becomes coated with metallic silver. Chapter 15 | Slide 27 of 36 Tests for Distinguishing between Aldehydes and Ketones • Benedict’s Test – Benedict’s reagent, which contains Cu+2, reacts with aldehydes that have an adjacent OH group – The aldehyde is oxidized and Cu+2 is reduced Cu2O, which appears as a brick red solid in the test tube – Ketones do not react. Chapter 15 | Slide 28 of 36 Aldehydes and Ketones → Fig. 15.9 Benedict’s solution turns brick red when an aldehyde reacts with it. Chapter 15 | Slide 29 of 36 Chapter 15 | Slide 30 of 36 Work on the following learning checks as homework. Chapter 15 | Slide 31 of 36 Learning Check Classify each as an aldehyde (1), ketone (2) or neither(3). O A. CH3CH2CCH3 CH3 B. CH3-O-CH3 O C. CH3-C-CH2CH D. CH3 Chapter 15 | Slide 32 of 36 Learning Check Name the following O A. CH3CH2CCH3 B. CH3 O C. CH3-C-CH2CH CH3 Chapter 15 | Slide 33 of 36 Learning Check Draw the structural formulas for each: A. 3-Methylpentanal B. 2,3-Dichloropropanal C. 3-Methyl-2-butanone Chapter 15 | Slide 34 of 36 Learning Check • Select the compound that would have the higher boiling point – A. CH3-CH2-CH3 or CH3-CH2-OH – B. CH3-CH2-OH or CH3-O-CH3 – C. O OR Chapter 15 | Slide 35 of 36 Learning Check • Are the following compounds soluble in water? – A. CH3-CH2-CH3 – B. CH3-CH2-OH – C. O – D. O Chapter 15 | Slide 36 of 36