Textbook Question
Draw the NMR spectrum expected from ethanol that has been shaken with a drop of D2O.
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Ch. 13 - Nuclear Magnetic Resonance Spectroscopy
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 13, Problem 23
Give the spectral assignments for the protons in isobutyl alcohol (Solved Problem 13-4). For example, Ha is a singlet, area = 1, at δ2.4.
Verified step by step guidance1
Step 1: Identify the structure of isobutyl alcohol (3-methylbutan-2-ol) and locate the different types of protons in the molecule. The molecule contains the following proton environments: Ha (hydroxyl proton), Hb (methylene protons), Hc (methine proton), and Hd (methyl protons).
Step 2: Assign the chemical shift (δ) values for each type of proton based on their electronic environment. Ha (hydroxyl proton) is deshielded due to the electronegativity of oxygen and typically appears around δ 2-4 ppm. Hb (methylene protons) are slightly deshielded due to their proximity to the hydroxyl group and appear around δ 3-4 ppm. Hc (methine proton) is deshielded due to the branching and appears around δ 1-2 ppm. Hd (methyl protons) are shielded and appear around δ 0.9-1.5 ppm.
Step 3: Determine the splitting pattern for each type of proton based on the number of neighboring protons (n+1 rule). Ha (hydroxyl proton) typically appears as a singlet due to rapid exchange with solvent. Hb (methylene protons) are split into a doublet by Hc. Hc (methine proton) is split into a multiplet by Hb and Hd. Hd (methyl protons) are split into a doublet by Hc.
Step 4: Assign the integration (area under the peak) for each type of proton based on the number of equivalent protons. Ha corresponds to 1 proton, Hb corresponds to 2 protons, Hc corresponds to 1 proton, and Hd corresponds to 6 protons (two equivalent methyl groups).
Step 5: Summarize the spectral assignments: Ha is a singlet, area = 1, at δ 2-4 ppm; Hb is a doublet, area = 2, at δ 3-4 ppm; Hc is a multiplet, area = 1, at δ 1-2 ppm; Hd is a doublet, area = 6, at δ 0.9-1.5 ppm.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Nuclear Magnetic Resonance (NMR) Spectroscopy
NMR spectroscopy is a powerful analytical technique used to determine the structure of organic compounds. It provides information about the number and environment of hydrogen atoms (protons) in a molecule, allowing chemists to identify different types of protons based on their chemical shifts (δ) and splitting patterns. Understanding NMR is crucial for interpreting the spectral data of isobutyl alcohol.
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General NMR Features
Chemical Shifts (δ)
Chemical shifts (δ) in NMR spectroscopy indicate the resonance frequency of a nucleus relative to a standard reference. They are measured in parts per million (ppm) and provide insight into the electronic environment surrounding the protons. Different functional groups and molecular environments lead to distinct chemical shifts, which are essential for assigning protons in isobutyl alcohol.
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Multiplicity and Integration
Multiplicity refers to the splitting pattern of NMR signals, which arises from the interaction of neighboring protons (n+1 rule). Integration indicates the relative number of protons contributing to a particular signal, providing information about the area under the peak. Together, these concepts help in identifying and assigning the protons in isobutyl alcohol, as seen in the spectral assignments.
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Related Practice
Textbook Question
Propose chemical structures consistent with the following NMR spectra and molecular formulas. In spectrum (a), explain why the peaks around δ1.65 and δ3.75 are not clean multiplets, but show complex splitting.
(a) <IMAGE>
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Textbook Question
Five proton NMR spectra are given here, together with molecular formulas. In each case, propose a structure that is consistent with the spectrum.
(b) <IMAGE>
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Textbook Question
Draw the expected NMR spectrum of methyl propionate, and point out how it differs from the spectrum of ethyl acetate.
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Textbook Question
(b) Draw the proton NMR spectrum you would expect for butan-2-one. How well do the proton chemical shifts predict the carbon chemical shifts using the "15 to 20 times as large" rule of thumb?
Textbook Question
(a) Show which carbon atoms correspond with which peaks in the 13C NMR spectrum of butan-2-one (Figure 13-45).
<IMAGE>
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