Textbook Question
How many sets of equivalent hydrogens are present in the molecule that resulted in this NMR spectrum? [Recall that some signals can be split into multiple peaks—they are still just one signal.]
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Ch. 15 - Structural Identification II: Nuclear Magnetic Resonance Spectroscopy
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. 15 - Structural Identification II: Nuclear Magnetic Resonance SpectroscopyProblem 19b
Mullins 1st EditionCh. 15 - Structural Identification II: Nuclear Magnetic Resonance SpectroscopyProblem 19bChapter 14, Problem 19b
For the molecules shown, give the number of signals expected and the relative ratio of the signal integrations.
(b) 
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Identify the unique hydrogen environments in the molecule. Each unique environment will give rise to a separate NMR signal.
Consider the symmetry of the molecule. Symmetrical molecules may have fewer unique hydrogen environments due to equivalent positions.
Count the number of hydrogens in each unique environment to determine the relative ratio of the signal integrations. This is because the area under each NMR signal is proportional to the number of hydrogens contributing to that signal.
Use the chemical structure to determine if any hydrogens are in similar electronic environments, which would result in them being equivalent and thus contributing to the same signal.
Summarize the number of signals and their relative integrations based on the analysis of unique hydrogen environments and their symmetry.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
NMR Spectroscopy
Nuclear Magnetic Resonance (NMR) spectroscopy is a technique used to determine the structure of organic compounds by analyzing the magnetic properties of atomic nuclei. In NMR, different environments of hydrogen atoms (protons) in a molecule produce distinct signals, allowing chemists to infer the number and type of hydrogen environments present.
Recommended video:
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10:06
General NMR Features
Chemical Shift
Chemical shift refers to the position of an NMR signal relative to a standard reference compound, typically tetramethylsilane (TMS). It provides information about the electronic environment surrounding a nucleus, with shifts influenced by factors such as electronegativity and hybridization of nearby atoms. Understanding chemical shifts helps predict the number of signals in an NMR spectrum.
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11:441H NMR Chemical Shifts
Signal Integration
Signal integration in NMR spectroscopy quantifies the area under each signal peak, which corresponds to the number of protons contributing to that signal. The relative ratio of signal integrations reflects the proportion of different types of protons in the molecule, aiding in the determination of molecular structure by indicating how many protons are in each distinct environment.
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06:461H NMR Integration
Related Practice
Textbook Question
The methyl hydrogens in propane appear at a chemical shift of 0.9 ppm, whereas the methyl hydrogens of propene appear around 2.5 ppm. Explain.
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Textbook Question
(a) Calculate the resonance frequency of an aldehydic proton ( δ 9.3 ppm) if it is detected on a 60-MHz NMR spectrometer.
(b) What if it were detected on a 300-MHz instrument?
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Textbook Question
If rotation is restricted, as in the case of the molecule shown, the hydrogens labeled a and b are nonequivalent. Why?
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Textbook Question
Without worrying about the relative location of the signals (i.e., the chemical shift) or the splitting patterns, draw a spectrum of the following molecule, being sure to indicate the integration of each peak. Label each signal based on the set of equivalent hydrogens to which it corresponds. [We expand on this question in future assessments.]
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Textbook Question
Without worrying about the relative location of the signals (i.e., the chemical shift) or the splitting patterns, draw a spectrum of the following molecule. Be sure to label each signal based on the set of equivalent hydrogens to which it corresponds.
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