Textbook Question
Identify the important bands you would expect to find in an IR spectrum for the following molecules.
(a)
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Ch. 14 - Structural Identification I: Infrared Spectroscopy and Mass Spectrometry
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471
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Table of contents
- Ch. 2 - General Chemistry Translated: Finding the Electrons114
- Ch. 3 - Alkanes and Cycloalkanes: Properties and Conformational Analysis109
- Ch. 4 - Acids and Bases: Electron Flow144
- Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics118
- Ch. 6 - Stereoisomerism: Arrangement of Atoms in Space112
- Ch. 7 - Principles of Green (Organic) Chemistry3
- Ch. 8 - Alkenes I: Properties and Electrophilic Additions158
- Ch. 9 - Alkenes II: Oxidation and Reduction150
- Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions101
- Ch. 11 - Properties and Synthesis of Alkyl Halides: Radical Reactions108
- Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes172
- Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination239
- Ch. 14 - Structural Identification I: Infrared Spectroscopy and Mass Spectrometry54
- Ch. 15 - Structural Identification II: Nuclear Magnetic Resonance Spectroscopy93
- Ch. 16 - Metals in Organic Chemistry48
- Ch. 17 - Carbonyl Addition Reactions: Aldehydes and Ketones45
- Ch. 18 - Nucleophilic Acyl Substitution I: Carboxylic Acids18
- Ch. 19 - Nucleophilic Acyl Substitution II: Carboxylic Acid Derivatives39
- Ch. 20 - Enolates: Carbonyl Addition and Substitution13
- Ch. 21 - Conjugated Systems I: Stability and Addition Reactions56
- Ch. 22 - Conjugated Systems II: Pericyclic Reactions54
- Ch. 23 - Benzene I: Aromatic Stability and Substitution Reactions64
- Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring62
- Ch. 25 - Amines: Structure, Reactions, and Synthesis27
- Ch. 26 - Amino Acids, Proteins, and Peptide Synthesis9
- Ch. 27 - Carbohydrates, Nucleic Acids, and Lipids54
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
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Mullins 1st EditionCh. 14 - Structural Identification I: Infrared Spectroscopy and Mass SpectrometryProblem 46e
Mullins 1st EditionCh. 14 - Structural Identification I: Infrared Spectroscopy and Mass SpectrometryProblem 46eChapter 13, Problem 46e
Based on Hooke's law, choose the bond in each pair that you expect to vibrate at a higher wavenumber.
(e) C=N vs C≡N
Verified step by step guidance1
Understand Hooke's Law in the context of molecular vibrations: Hooke's Law relates the vibrational frequency of a bond to the force constant (k) and the reduced mass (μ) of the atoms involved. The formula is given by: , where v is the vibrational frequency.
Identify the bonds in question: We have a C=N bond (a double bond) and a C≡N bond (a triple bond).
Consider the force constant (k): Triple bonds generally have a higher force constant than double bonds because they are stronger and stiffer. This means that the C≡N bond will have a higher force constant compared to the C=N bond.
Evaluate the reduced mass (μ): The reduced mass is calculated using the formula , where m1 and m2 are the masses of the atoms involved. Since both bonds involve the same atoms (carbon and nitrogen), the reduced mass will be the same for both bonds.
Determine which bond vibrates at a higher wavenumber: Since the C≡N bond has a higher force constant and the same reduced mass as the C=N bond, it will vibrate at a higher wavenumber according to Hooke's Law.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Hooke's Law in Vibrational Spectroscopy
Hooke's Law relates the vibrational frequency of a bond to the bond strength and the masses of the atoms involved. In vibrational spectroscopy, stronger bonds and lighter atoms result in higher vibrational frequencies, which correspond to higher wavenumbers in IR spectra.
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The Beer-Lambert Law Concept 2
Bond Order and Strength
Bond order refers to the number of chemical bonds between a pair of atoms. A higher bond order typically indicates a stronger bond. For example, a triple bond (C≡N) is stronger than a double bond (C=N), leading to higher vibrational frequencies and wavenumbers.
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Wavenumber in IR Spectroscopy
Wavenumber is a measure of frequency used in infrared spectroscopy, expressed in reciprocal centimeters (cm⁻¹). It indicates the energy of molecular vibrations; higher wavenumbers correspond to higher energy vibrations, often seen in stronger bonds like triple bonds compared to double bonds.
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Related Practice
Textbook Question
Identify the peaks in the mass spectrum of octan-4-one that correspond to (b) the McLafferty rearrangement.
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Textbook Question
Based on Hooke's law, choose the bond in each pair that you expect to vibrate at a higher wavenumber.
(f) C―S vs C=O
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Textbook Question
2-Methylnonan-4-one can undergo two different McLafferty rearrangements. Draw the products of each of them.
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Textbook Question
Choose the bond in each pair that you expect to have the more intense stretching band
(b) C=O vs. C=N
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Textbook Question
Assign the structure based on the mass spectrum and IR spectrum shown.
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