Textbook Question
Propose a mechanism for the acid-catalyzed bromination of pentan-3-one.
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Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
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Wade 9th EditionCh. 22 - Condensations and Alpha Substitutions of Carbonyl CompoundsProblem 14
Wade 9th EditionCh. 22 - Condensations and Alpha Substitutions of Carbonyl CompoundsProblem 14Chapter 22, Problem 14
Which compounds will give positive iodoform tests?
(a) 1-phenylethanol
(b) pentan-2-one
(c) pentan-2-ol
(d) pentan-3-one
(e) acetone
(f) isopropyl alcohol
Verified step by step guidance1
Step 1: Understand the iodoform test. The iodoform test is used to identify compounds containing a methyl group directly attached to a carbonyl group (C=O) or a methyl group attached to a hydroxyl group (-OH) in secondary alcohols. These compounds produce a yellow precipitate of iodoform (CHI3) when treated with iodine and a base.
Step 2: Analyze compound (a) 1-phenylethanol. This compound contains a hydroxyl group (-OH) attached to a carbon that is directly bonded to a methyl group. Since it meets the criteria for the iodoform test, it will give a positive result.
Step 3: Analyze compound (b) pentan-2-one. This compound contains a methyl group directly attached to a carbonyl group (C=O). Therefore, it will give a positive iodoform test.
Step 4: Analyze compound (c) pentan-2-ol. This compound contains a hydroxyl group (-OH) attached to a carbon that is directly bonded to a methyl group. It meets the criteria for the iodoform test and will give a positive result.
Step 5: Analyze compound (d) pentan-3-one, (e) acetone, and (f) isopropyl alcohol. Pentan-3-one does not have a methyl group directly attached to the carbonyl group, so it will not give a positive test. Acetone has a methyl group attached to the carbonyl group and will give a positive test. Isopropyl alcohol has a methyl group attached to the hydroxyl group and will also give a positive test.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Iodoform Test
The iodoform test is a qualitative test used to identify the presence of methyl ketones or secondary alcohols that can be oxidized to methyl ketones. A positive result is indicated by the formation of a yellow precipitate of iodoform (CHI3) when the compound is treated with iodine and a base. This test is particularly useful in distinguishing compounds with specific structural features.
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Methyl Ketones
Methyl ketones are a class of ketones that contain a methyl group (–CH3) adjacent to the carbonyl group (C=O). Compounds such as acetone and pentan-2-one are examples of methyl ketones, which will yield a positive iodoform test. The presence of this structural feature is crucial for the reactivity in the iodoform reaction.
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Secondary Alcohols
Secondary alcohols are alcohols where the hydroxyl group (–OH) is attached to a carbon atom that is connected to two other carbon atoms. Compounds like 1-phenylethanol and isopropyl alcohol are secondary alcohols that can be oxidized to form methyl ketones, thus giving a positive iodoform test. Understanding the classification of alcohols is essential for predicting their behavior in chemical tests.
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Related Practice
Textbook Question
Predict the products of the following reactions.
(a) cyclopentyl methyl ketone + excess Cl2 + excess NaOH
(b) 1-cyclopentylethanol + excess I2 + excess NaOH
(c) propiophenone + excess Br2 + excess NaOH
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Textbook Question
Propose a mechanism to show how acetophenone undergoes base-promoted chlorination to give trichloroacetophenone.
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Textbook Question
Propose a mechanism for the reaction of cyclohexyl methyl ketone with excess bromine in the presence of sodium hydroxide.
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Textbook Question
Show the products of the reactions of these carboxylic acids with PBr3/Br2 before and after hydrolysis.
(a) pentanoic acid
(b) phenylacetic acid
(c) succinic acid
(d) oxalic acid
Textbook Question
Acid-catalyzed halogenation is synthetically useful for converting ketones to α,β-unsaturated ketones, which are useful in Michael reactions (Section 22-18). Propose a method for converting cyclohexanone to cyclohex-2-en-1-one, an important synthetic starting material.
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