Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

15. Analytical Techniques:IR, NMR, Mass Spect

NMR Practice

Organic Chemistry

15. Analytical Techniques:IR, NMR, Mass Spect

NMR Practice

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4:22 minutes

Problem 23

Textbook Question

Give the spectral assignments for the protons in isobutyl alcohol (Solved Problem 13-4). For example, H^a is a singlet, area = 1, at δ2.4.

Verified step by step guidance

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.

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.

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

Sketch your predictions of the proton NMR spectra of the following compounds.

(a) CH₃–O–CH₂CH₃

Textbook Question

The following proton NMR spectrum is of a compound of molecular formula C₃H₈O.

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(a) Propose a structure for this compound.

(b) Assign peaks to show which protons give rise to which signals in the spectrum.

Textbook Question

An unknown compound has the molecular formula C₉H₁₁Br. Its proton NMR spectrum shows the following absorptions:

singlet, δ7.1, integral 44 mm

singlet, δ2.3, integral 130 mm

singlet, δ2.2, integral 67 mm

Propose a structure for this compound.

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>

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>

Textbook Question

Draw the NMR spectra you expect for the following compounds.

(b)

Textbook Question

Draw the NMR spectra you expect for the following compounds.

(a)

Textbook Question

Identify each of the following compounds from its molecular formula and its ¹H NMR spectrum:

b. C₆H₁₂O

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