Textbook Question
A compound gives a mass spectrum with essentially only three peaks at m/z = 77 (40%), 112 (100%), and 114 (33%). Identify the compound.
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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 55
Bruice 8th EditionCh. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis SpectroscopyProblem 55Chapter 14, Problem 55
Rank the following compounds from highest wavenumber to lowest wavenumber for their C=O absorption band:
Verified step by step guidance1
Step 1: Understand the concept of C=O absorption band in IR spectroscopy. The wavenumber of the C=O stretch depends on factors such as conjugation, inductive effects, and hydrogen bonding. Higher wavenumbers correspond to stronger bonds or less conjugation.
Step 2: Analyze the structures provided. The first compound is a ketone with two alkyl groups attached to the carbonyl carbon. The second compound is an aldehyde with one alkyl group and one hydrogen attached to the carbonyl carbon. The third compound is formaldehyde, with two hydrogens attached to the carbonyl carbon.
Step 3: Consider the inductive effects. Alkyl groups donate electron density to the carbonyl group, weakening the C=O bond and lowering the wavenumber. Hydrogen atoms do not have this electron-donating effect, so formaldehyde will have the highest wavenumber.
Step 4: Rank the compounds based on conjugation and inductive effects. Formaldehyde (third compound) has the highest wavenumber due to the absence of electron-donating alkyl groups. The aldehyde (second compound) has a lower wavenumber than formaldehyde but higher than the ketone (first compound), which has two electron-donating alkyl groups.
Step 5: Final ranking from highest wavenumber to lowest wavenumber: Formaldehyde > Aldehyde > Ketone.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
C=O Stretching Frequency
The C=O bond exhibits a characteristic stretching frequency that can be measured in wavenumbers (cm⁻¹). This frequency is influenced by the nature of the surrounding atoms and groups, with stronger bonds and less steric hindrance typically resulting in higher wavenumbers. In general, carbonyl compounds with electron-withdrawing groups show higher wavenumber absorption due to increased bond strength.
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Common IR Frequencies
Inductive Effect
The inductive effect refers to the electron-withdrawing or electron-donating influence of substituents on a molecule. Electron-withdrawing groups, such as halogens or carbonyls, increase the positive character of the carbonyl carbon, leading to a stronger C=O bond and thus a higher wavenumber in IR spectroscopy. Conversely, electron-donating groups can lower the wavenumber by weakening the C=O bond.
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01:47Understanding the Inductive Effect.
Steric Hindrance
Steric hindrance occurs when bulky groups around a reactive site impede the approach of other molecules or groups. In the context of carbonyl compounds, increased steric hindrance can lower the frequency of the C=O stretching vibration due to the reduced ability of the bond to stretch freely. This effect is particularly relevant when comparing carbonyls with different substituents, as larger groups can lead to lower wavenumber absorptions.
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02:53Understanding steric effects.
Related Practice
Textbook Question
Rank the following compounds from highest wavenumber to lowest wavenumber for their C-O absorption band:
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Textbook Question
What hydrocarbons that contain a six-membered ring will have a molecular ion peak at m/z = 112?
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Textbook Question
The mass spectrum for a compound with molecular weight of 102 is shown below. Its IR spectrum has a broad, strong absorption at 3600 cm–1 and a medium absorption at 1360 cm–1.
a. Identify the compound.
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Textbook Question
The mass spectrum for a compound with molecular weight of 102 is shown below. Its IR spectrum has a broad, strong absorption at 3600 cm–1 and a medium absorption at 1360 cm–1.
b. Show the mechanism for formation of the peak at m/z = 84.
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Textbook Question
A mass spectrum shows significant peaks at m/z = 87, 115, 140, and 143. Which of the following compounds is responsible for that mass spectrum?
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