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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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 30c,d
Bruice 8th EditionCh. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis SpectroscopyProblem 30c,dChapter 14, Problem 30c,d
For each of the following pairs of compounds, name one absorption band that can be used to distinguish between them.
c. 
d. 
Verified step by step guidance1
Step 1: Analyze the first pair of compounds (I). The first compound is cyclopentane, a saturated cyclic hydrocarbon, while the second compound is methylcyclopentane, which has a methyl group attached to the cyclopentane ring.
Step 2: Identify the functional groups or structural differences in the first pair. Cyclopentane lacks any substituents, while methylcyclopentane has a methyl group (-CH₃). This difference can be detected using IR spectroscopy by looking for the C-H stretching vibrations of the methyl group.
Step 3: In IR spectroscopy, the methyl group in methylcyclopentane will show absorption bands around 1375 cm⁻¹ and 1450 cm⁻¹ due to C-H bending vibrations, which are absent in cyclopentane.
Step 4: Analyze the second pair of compounds (II). Both compounds are alkynes, but the first compound is a terminal alkyne (with a hydrogen attached to the triple bond), while the second compound is an internal alkyne (with no hydrogen attached to the triple bond).
Step 5: In IR spectroscopy, terminal alkynes exhibit a sharp absorption band around 3300 cm⁻¹ due to the C-H stretching vibration of the terminal alkyne hydrogen. This band is absent in internal alkynes, which can be used to distinguish between the two compounds.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Infrared (IR) Spectroscopy
IR spectroscopy is a technique used to identify functional groups in organic compounds by measuring the absorption of infrared light. Different bonds absorb characteristic frequencies of IR radiation, leading to distinct absorption bands in the spectrum. This method is crucial for distinguishing between compounds based on their molecular vibrations.
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General Features of IR Spect
Functional Groups
Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. In the context of IR spectroscopy, the presence of different functional groups, such as alkenes, alkynes, or cyclic structures, can lead to unique absorption bands that help differentiate between compounds.
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Absorption Bands
Absorption bands in an IR spectrum correspond to specific vibrational transitions of molecular bonds. Each type of bond (e.g., C-H, C=C, C≡C) has a unique absorption frequency, allowing chemists to identify and distinguish between compounds. Recognizing these bands is essential for interpreting IR spectra and determining the structure of organic molecules.
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Related Practice
Textbook Question
Identify the compound that gives the mass spectrum and infrared spectrum shown here.
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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
For each of the following pairs of compounds, name one absorption band that can be used to distinguish between them.
e.
f.
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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
Which of the following compounds has a vibration that is infrared inactive?
1-butyne, 2-butyne, H2, H2O, Cl2, ethene
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