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 17
Mullins 1st EditionCh. 15 - Structural Identification II: Nuclear Magnetic Resonance SpectroscopyProblem 17Chapter 14, Problem 17
If rotation is restricted, as in the case of the molecule shown, the hydrogens labeled a and b are nonequivalent. Why?
Verified step by step guidance1
Begin by understanding the concept of restricted rotation in organic molecules. Restricted rotation often occurs due to the presence of a double bond or a ring structure, which prevents free rotation around the bond.
Consider the molecule in question. Identify any structural features that might restrict rotation, such as a double bond or a cyclic structure. These features create a fixed spatial arrangement of atoms.
Examine the positions of the hydrogens labeled 'a' and 'b'. Due to restricted rotation, these hydrogens are locked in specific spatial orientations relative to other groups in the molecule.
Understand that nonequivalent hydrogens are those that occupy different chemical environments. Restricted rotation can lead to different environments for hydrogens 'a' and 'b', as they cannot interchange positions due to the fixed structure.
Conclude that the hydrogens labeled 'a' and 'b' are nonequivalent because they are in different chemical environments, resulting from the restricted rotation that prevents them from being in the same spatial orientation or chemical environment.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Restricted Rotation
Restricted rotation in organic molecules often occurs due to the presence of double bonds or ring structures, which prevent free rotation around the bond axis. This restriction leads to fixed spatial arrangements of atoms, affecting the chemical environment and properties of the molecule.
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05:43
Specific rotation vs. observed rotation.
Stereochemistry
Stereochemistry involves the study of the spatial arrangement of atoms in molecules and how this affects their chemical behavior. In molecules with restricted rotation, different spatial arrangements can lead to stereoisomers, which have distinct properties despite having the same molecular formula.
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Chemical Equivalence
Chemical equivalence refers to atoms or groups in a molecule that are in identical environments and thus exhibit the same chemical behavior. In cases of restricted rotation, such as in double bonds, atoms like hydrogens can become nonequivalent due to differing spatial environments, leading to unique chemical shifts in spectroscopy.
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Related Practice
Textbook Question
For the molecules shown, give the number of signals expected and the relative ratio of the signal integrations.
(b)
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Textbook Question
How many unique ¹H NMR signals would you expect in an NMR spectrum for the following molecules?
(c)
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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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Textbook Question
How many unique ¹H NMR signals would you expect in an NMR spectrum for the following molecules?
(b)