Textbook Question
Draw the NMR spectrum expected from ethanol that has been shaken with a drop of D2O.
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Ch. 13 - Nuclear Magnetic Resonance Spectroscopy
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 13, Problem 19a,b
Propose mechanisms to show the interchange of protons between ethanol molecules under
(a) acid catalysis.
(b) base catalysis.
Verified step by step guidance1
Under acid catalysis: Begin by recognizing that the catalyst is an acid, which donates a proton (H⁺). The first step involves the protonation of one ethanol molecule (CH₃CH₂OH) by the acid, forming a positively charged oxonium ion (CH₃CH₂OH₂⁺).
Under acid catalysis: Next, another ethanol molecule acts as a nucleophile, using its lone pair of electrons on the oxygen atom to attack the oxonium ion. This results in the transfer of a proton from the oxonium ion to the second ethanol molecule, regenerating the neutral ethanol and forming a new oxonium ion.
Under base catalysis: Recognize that the catalyst is a base, which accepts a proton. The first step involves the deprotonation of one ethanol molecule (CH₃CH₂OH) by the base, forming an ethoxide ion (CH₃CH₂O⁻) and water (H₂O).
Under base catalysis: The ethoxide ion then acts as a strong base and abstracts a proton from another ethanol molecule, regenerating the neutral ethanol and forming a new ethoxide ion.
In both cases, the interchange of protons between ethanol molecules is facilitated by the catalyst (acid or base), which lowers the activation energy for the proton transfer and ensures the reaction proceeds efficiently.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Proton Transfer Mechanism
Proton transfer mechanisms involve the movement of protons (H⁺ ions) between molecules, which is fundamental in acid-base chemistry. In the context of ethanol, this process can be facilitated by either an acid or a base, leading to the formation of protonated or deprotonated species. Understanding this mechanism is crucial for analyzing how ethanol molecules interact under different catalytic conditions.
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Acid Catalysis
Acid catalysis refers to the acceleration of a chemical reaction by the addition of an acid, which donates protons to the reactants. In the case of ethanol, an acid catalyst can protonate the hydroxyl group, enhancing the nucleophilicity of the ethanol molecule and facilitating proton transfer between ethanol molecules. This concept is essential for understanding how acids influence the reactivity of alcohols.
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Base Catalysis
Base catalysis involves the use of a base to increase the rate of a reaction by accepting protons from the reactants. In the context of ethanol, a base can deprotonate the hydroxyl group, generating an alkoxide ion that can participate in proton transfer with other ethanol molecules. This concept is vital for comprehending how bases alter the behavior of alcohols in chemical reactions.
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Related Practice
Textbook Question
Propose chemical structures consistent with the following NMR spectra and molecular formulas. In spectrum (a), explain why the peaks around δ1.65 and δ3.75 are not clean multiplets, but show complex splitting.
(a) <IMAGE>
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Textbook Question
Predict the theoretical number of different NMR signals produced by each compound, and give approximate chemical shifts. Point out any diastereotopic relationships.
c. Ph—CHBr—CH2Br
d. vinyl chloride
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Textbook Question
Draw the expected NMR spectrum of methyl propionate, and point out how it differs from the spectrum of ethyl acetate.
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Textbook Question
If the imaginary replacement of either of two protons forms enantiomers, then those protons are said to be enantiotopic. The NMR is not a chiral probe, and it cannot distinguish between enantiotopic protons. They are seen to be “equivalent by NMR.”
(a) Use the imaginary replacement technique to show that the two allylic protons (those on C3) of allyl bromide are enantiotopic.
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Textbook Question
Predict the theoretical number of different NMR signals produced by each compound, and give approximate chemical shifts. Point out any diastereotopic relationships.
a. 2-bromobutane
b. cyclopentanol
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