Textbook Question
Explain why we speak of acidic hydrolysis of an ester as acid-catalyzed, but of basic hydrolysis as base-promoted.
Ch. 21 - Carboxylic Acid Derivatives
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
Chapter 21, Problem 16b
Suppose we have some optically pure (R)-2-butyl acetate that has been "labeled" with the heavy 18O isotope at one oxygen atom as shown.
(b) Repeat part (a) for the acid-catalyzed hydrolysis of this compound.
Verified step by step guidance1
Step 1: Recognize that the reaction involves acid-catalyzed hydrolysis of an ester. The ester bond will be cleaved, resulting in the formation of an alcohol and a carboxylic acid.
Step 2: Understand the mechanism of acid-catalyzed hydrolysis. The reaction begins with protonation of the carbonyl oxygen by the acid catalyst (H+), increasing the electrophilicity of the carbonyl carbon.
Step 3: Water acts as a nucleophile and attacks the carbonyl carbon, forming a tetrahedral intermediate. This intermediate contains both the original ester oxygen and the oxygen from water.
Step 4: The tetrahedral intermediate undergoes proton transfer and elimination of the leaving group (the alcohol), resulting in the formation of the carboxylic acid. The heavy isotope O-18 will remain attached to the alcohol group, not the carboxylic acid.
Step 5: Analyze the stereochemistry of the alcohol product. The (R)-configuration of the original compound will be retained in the alcohol product, as the hydrolysis does not affect the stereocenter.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Optical Purity and Chirality
Optical purity refers to the proportion of one enantiomer over another in a chiral compound, which can rotate plane-polarized light. Chirality is a property of a molecule that makes it non-superimposable on its mirror image, often due to the presence of a chiral center, typically a carbon atom bonded to four different substituents. Understanding these concepts is crucial for analyzing reactions involving chiral molecules, such as (R)-2-butyl acetate.
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What is chirality?
Acid-Catalyzed Hydrolysis
Acid-catalyzed hydrolysis is a reaction where an ester is converted into an alcohol and a carboxylic acid in the presence of an acid catalyst, typically a strong acid like HCl or H2SO4. The acid protonates the carbonyl oxygen, increasing the electrophilicity of the carbonyl carbon, facilitating nucleophilic attack by water. This process is essential for understanding how the labeled (R)-2-butyl acetate reacts in the presence of water and acid.
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Isotope Labeling
Isotope labeling involves substituting a specific atom in a molecule with a heavier isotope, such as O-18 instead of the more common O-16. This technique is used to trace the movement of atoms through a reaction mechanism, providing insights into reaction pathways and mechanisms. In the context of the hydrolysis of (R)-2-butyl acetate, the presence of O-18 allows for tracking the fate of the oxygen atom during the reaction.
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03:06Understanding the hydrogen isotopes.
Related Practice
Textbook Question
Propose a mechanism for the following ring-opening transesterification. Use the mechanism in Problem 21-13 as a model.
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Textbook Question
Suppose we have some optically pure (R)-2-butyl acetate that has been 'labeled' with the heavy 18O isotope at one oxygen atom as shown.
(c) Explain how you would prove experimentally where the 18O label appears in the products. (18O is not radioactive.)
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Textbook Question
Soap manufacturers always use base to hydrolyze fats, and never acid. Suggest two reasons that basic hydrolysis is preferred.
Textbook Question
1. Propose a mechanism for the acid-catalyzed reaction of salicylic acid with acetic anhydride.
2. Explain why a single drop of sulfuric acid dramatically increases the reaction rate.
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Textbook Question
Suppose we have some optically pure (R)-2-butyl acetate that has been 'labeled' with the heavy 18O isotope at one oxygen atom as shown.
(a) Draw a mechanism for the hydrolysis of this compound under basic conditions. Predict which of the products will contain the 18O label. Also predict whether the butan-2-ol product will be pure (R), pure (S), or racemized.
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