Textbook Question
Rank the following compounds from highest wavenumber to lowest wavenumber for their C=O absorption bands:
b.
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Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy
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. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis SpectroscopyProblem 26
Bruice 8th EditionCh. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis SpectroscopyProblem 26Chapter 14, Problem 26
Which shows an O–H stretch at a larger wavenumber: ethanol dissolved in carbon disulfide or an undiluted sample of ethanol?
Verified step by step guidance1
Understand the concept of hydrogen bonding: The O-H stretch in an IR spectrum is influenced by hydrogen bonding. Stronger hydrogen bonding lowers the wavenumber of the O-H stretch due to the weakening of the O-H bond.
Analyze the environment of ethanol in carbon disulfide: When ethanol is dissolved in carbon disulfide (CS₂), a non-polar solvent, hydrogen bonding between ethanol molecules is disrupted because CS₂ does not participate in hydrogen bonding.
Analyze the environment of undiluted ethanol: In an undiluted sample of ethanol, ethanol molecules are in close proximity and can form strong intermolecular hydrogen bonds with each other.
Compare the effects on the O-H stretch: In the case of ethanol dissolved in CS₂, the O-H bond is less involved in hydrogen bonding, so the O-H stretch appears at a higher wavenumber. In undiluted ethanol, the strong hydrogen bonding shifts the O-H stretch to a lower wavenumber.
Conclude: Ethanol dissolved in carbon disulfide shows an O-H stretch at a larger wavenumber compared to undiluted ethanol due to the absence of significant hydrogen bonding in the dissolved state.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Infrared Spectroscopy
Infrared spectroscopy is a technique used to identify molecular structures by measuring the absorption of infrared light, which causes molecular vibrations. Different functional groups absorb light at characteristic wavenumbers, allowing for the identification of specific bonds, such as O-H stretches in alcohols.
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Hydrogen Bonding
Hydrogen bonding occurs when a hydrogen atom covalently bonded to a highly electronegative atom, like oxygen, interacts with another electronegative atom. In ethanol, hydrogen bonding can affect the O-H stretch frequency; stronger hydrogen bonding typically results in a lower wavenumber due to increased bond strength and reduced vibrational frequency.
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00:48The definition of hydrogenation.
Solvent Effects
The choice of solvent can significantly influence the vibrational frequencies observed in infrared spectroscopy. In non-polar solvents like carbon disulfide, ethanol's hydrogen bonding interactions are diminished, potentially leading to a higher wavenumber for the O-H stretch compared to undiluted ethanol, where strong intermolecular hydrogen bonds are present.
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Related Practice
Textbook Question
How can IR spectroscopy be used to distinguish between the following compounds?
e. cyclohexene and cyclohexane
f. a primary amine and a tertiary amine
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Textbook Question
Which occurs at a larger wavenumber:
a. the C–O stretch of phenol or the C–O stretch of cyclohexanol?
b. the C=O stretch of a ketone or the C=O stretch of an amide?
c. the C–N stretch of cyclohexylamine or the C–N stretch of aniline?
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Textbook Question
How can IR spectroscopy be used to distinguish between the following compounds?
a. a ketone and an aldehyde
b. a cyclic ketone and an open-chain ketone
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Textbook Question
A nitrogen-containing compound shows no absorption band at ~3400 cm-1 and no absorption bands between ~1700 cm-1 and ~1600 cm-1 or between 2260 cm-1 and 2220 cm-1. What class of compound is it?
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Textbook Question
Why is the C–O absorption band of 1-hexanol at a smaller wavenumber (1060 cm–1) than the C–O absorption band of pentanoic acid (1220 cm–1)?
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