Textbook Question
Propose a mechanism for the base-promoted hydrolysis of γ-butyrolactone:
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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 16c
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.)
Verified step by step guidance1
Step 1: Understand the structure of the compound provided. The molecule is (R)-2-butyl acetate, which is an ester. The heavy isotope O-18 is labeled on the oxygen atom connected to the butyl group (the alkoxy oxygen). This labeling is crucial for tracking the fate of the O-18 during chemical reactions.
Step 2: Plan an experiment to track the O-18 label. Hydrolysis of the ester is a common method to break it down into its components. When hydrolyzed under acidic or basic conditions, the ester will produce an alcohol (2-butanol) and a carboxylic acid (acetic acid). The goal is to determine which product contains the O-18 label.
Step 3: Perform the hydrolysis reaction. Use either acidic or basic conditions to hydrolyze the ester. For example, in acidic hydrolysis, the ester reacts with water to form the alcohol and carboxylic acid. Ensure the reaction is complete to isolate the products.
Step 4: Analyze the products using mass spectrometry. Mass spectrometry is a powerful tool for detecting isotopes like O-18. Analyze both the alcohol (2-butanol) and the carboxylic acid (acetic acid) to determine which one contains the O-18 label. The mass spectrum will show a peak corresponding to the molecular weight of the compound with the O-18 isotope.
Step 5: Interpret the results. Based on the mechanism of ester hydrolysis, the O-18 label should remain with the oxygen atom that was originally part of the ester bond. This means the O-18 label will appear in the carboxylic acid (acetic acid) product. Confirm this by comparing the mass spectrometry data of the products.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Isotope Labeling
Isotope labeling involves substituting a stable isotope, such as O-18, for a naturally occurring isotope in a molecule. This technique allows chemists to trace the movement and incorporation of the labeled atom during chemical reactions. In this case, the O-18 label in (R)-2-butyl acetate can help identify which products contain the heavy oxygen, providing insights into reaction mechanisms and pathways.
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Mass Spectrometry
Mass spectrometry (MS) is an analytical technique used to measure the mass-to-charge ratio of ions. It can effectively distinguish between molecules based on their mass, allowing for the identification of products containing the O-18 label. By comparing the mass spectra of the reaction products, one can determine which species incorporate the heavy isotope, thus proving where the O-18 label appears.
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Nuclear Magnetic Resonance (NMR) Spectroscopy
Nuclear Magnetic Resonance (NMR) spectroscopy is a powerful technique used to determine the structure of organic compounds. In the context of isotope labeling, NMR can provide information about the chemical environment of the labeled oxygen atom. By analyzing the NMR spectra of the products, one can infer the presence of O-18 based on shifts in chemical shifts or coupling patterns, confirming the location of the label.
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Related Practice
Textbook Question
Explain why we speak of acidic hydrolysis of an ester as acid-catalyzed, but of basic hydrolysis as base-promoted.
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.
(b) Repeat part (a) for the acid-catalyzed hydrolysis of this compound.
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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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