Textbook Question
Explain why the acid-catalyzed dehydration of an alcohol is a reversible reaction, whereas the base-promoted dehydrohalogenation of an alkyl halide is an irreversible reaction.
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Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
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Bruice 8th EditionCh. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing CompoundsProblem 68
Bruice 8th EditionCh. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing CompoundsProblem 68Chapter 11, Problem 68
Explain why (S)-2-butanol forms a racemic mixture when it is heated in sulfuric acid.
Verified step by step guidance1
Understand the structure of (S)-2-butanol: It is a chiral alcohol with the hydroxyl group (-OH) attached to the second carbon of a four-carbon chain. The (S) configuration indicates that the molecule has a specific spatial arrangement around the chiral center.
Recognize the role of sulfuric acid: Sulfuric acid is a strong acid that can protonate the hydroxyl group of (S)-2-butanol, converting it into a better leaving group (water). This step facilitates the formation of a carbocation intermediate.
Describe the formation of the carbocation: When the hydroxyl group is protonated, it leaves as water, resulting in the formation of a planar carbocation at the second carbon. This carbocation is sp² hybridized and has a trigonal planar geometry, making it achiral.
Explain the racemization process: Because the carbocation is planar, the nucleophile (in this case, water or another molecule) can attack from either side of the plane with equal probability. This leads to the formation of both (R)-2-butanol and (S)-2-butanol in equal amounts, resulting in a racemic mixture.
Conclude the reasoning: The racemic mixture forms because the intermediate carbocation is achiral and allows for non-stereoselective attack by the nucleophile, producing both enantiomers in equal proportions.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Chirality and Stereoisomers
Chirality refers to the property of a molecule that makes it non-superimposable on its mirror image, leading to the existence of stereoisomers. (S)-2-butanol is a chiral molecule, meaning it has a specific three-dimensional arrangement that can exist in two enantiomeric forms. Understanding chirality is essential to grasp how reactions involving chiral centers can lead to the formation of racemic mixtures.
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What is chirality?
Racemic Mixture
A racemic mixture is a 1:1 mixture of two enantiomers of a chiral compound, resulting in no optical activity. When (S)-2-butanol is heated in sulfuric acid, it can undergo dehydration to form a carbocation intermediate, which can then be attacked by nucleophiles from either side, leading to the formation of both (S)- and (R)-2-butanol. This process illustrates how racemic mixtures can arise from chiral starting materials.
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Carbocation Stability and Rearrangement
Carbocations are positively charged species that can undergo rearrangements to form more stable structures. In the case of (S)-2-butanol, heating in sulfuric acid generates a carbocation that can rearrange or react in a way that allows for the formation of both enantiomers. The stability of the carbocation and the possibility of different pathways contribute to the racemic outcome of the reaction.
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Related Practice
Textbook Question
a. Draw the product or products that will be obtained from the reaction of cis-2-butene and trans-2-butene with each of the following reagents. If a product can exist as stereoisomers, show which stereoisomers are formed.
8. CH3OH + H2SO4
b. With which reagents do the two alkenes react to form different products?
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Textbook Question
In Section 10.12, we saw that S-adenosylmethionine (SAM) methylates the nitrogen atom of noradrenaline to form adrenaline, a more potent hormone. If SAM methylates an OH group attached to the benzene ring instead, it completely destroys noradrenaline's activity.
b. Which reaction is more apt to occur, methylation on nitrogen or methylation on oxygen?
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Textbook Question
Fill in each box with the appropriate reagent:
a.
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Textbook Question
Fill in each box with the appropriate reagent:
c.
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Textbook Question
An unknown alcohol with a molecular formula of C7H14O was oxidized to an aldehyde with HOCl. When an acidic solution of the alcohol was distilled, two alkenes were obtained. The alkene formed in greater yield was determined to be 1-methylcyclohexene. The other alkene formed the original un-known alcohol when treated with BH3/THF followed by H2O2, HO-, and H2O. Identify the unknown alcohol.
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