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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3:54 minutes

Problem 33

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.

Verified step by step guidance

Step 1: Analyze the molecular formula C9H11Br. This indicates the compound contains 9 carbon atoms, 11 hydrogen atoms, and 1 bromine atom. The presence of bromine suggests the compound may be an alkyl bromide or an aromatic bromine derivative.

Step 2: Examine the proton NMR data. The spectrum shows three singlets, which suggests that the hydrogens are in distinct environments and do not couple with neighboring hydrogens. This is indicative of isolated groups or symmetrical environments.

Step 3: Interpret the chemical shifts (δ values). The singlet at δ7.1 is characteristic of aromatic hydrogens, suggesting the presence of a benzene ring. The singlets at δ2.3 and δ2.2 are in the aliphatic region, indicating hydrogens attached to sp3 carbons.

Step 4: Consider the integrals. The integral values correspond to the relative number of hydrogens in each environment. The singlet at δ7.1 (44 mm) corresponds to 4 hydrogens, which is unusual for a benzene ring unless it is substituted. The singlet at δ2.3 (130 mm) corresponds to 6 hydrogens, likely from two equivalent methyl groups. The singlet at δ2.2 (67 mm) corresponds to 1 hydrogen, possibly from a methine group.

Step 5: Propose a structure. Based on the data, the compound likely contains a benzene ring substituted with a bromine atom and an isopropyl group (C(CH3)2H). The benzene ring accounts for the aromatic hydrogens, the isopropyl group accounts for the aliphatic hydrogens, and the bromine atom completes the molecular formula.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Molecular Formula Interpretation

The molecular formula C9H11Br indicates the compound contains 9 carbon atoms, 11 hydrogen atoms, and 1 bromine atom. Understanding the molecular formula is crucial for deducing the possible structure of the compound, as it provides insight into the degree of saturation and the presence of functional groups. The ratio of hydrogen to carbon suggests the compound may contain rings or multiple bonds.

Proton NMR Spectroscopy

Proton NMR (Nuclear Magnetic Resonance) spectroscopy is a technique used to determine the structure of organic compounds by analyzing the environment of hydrogen atoms in the molecule. The chemical shifts (δ) indicate the electronic environment of the protons, while the integrals provide information about the number of protons contributing to each signal. In this case, the three singlets at different δ values suggest distinct environments for the hydrogen atoms.

Integration and Splitting Patterns

In NMR spectroscopy, integration refers to the area under the peaks, which correlates to the number of protons contributing to that signal. The singlet nature of the peaks indicates that the protons are not coupled to neighboring protons, suggesting they are in isolated environments. Analyzing the integrals (44 mm, 130 mm, and 67 mm) helps in determining the relative number of protons in each environment, which is essential for constructing the molecular structure.

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Guided course

08:06

Common Splitting Patterns

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Related Practice

Textbook Question

Tell precisely how you would use the proton NMR spectra to distinguish between the following pairs of compounds.

(a) 1-bromopropane and 2-bromopropane

Textbook Question

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

(b)

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.

<IMAGE>

(a) Propose a structure for this compound.

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

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

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.

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)

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