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

Infrared Spectroscopy Table

Organic Chemistry

15. Analytical Techniques:IR, NMR, Mass Spect

Infrared Spectroscopy Table

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7:11 minutes

Problem 7

Textbook Question

The IR spectrum of trans-oct-2-enoic acid is shown. Point out the spectral characteristics that allow you to tell that this is a carboxylic acid, and show which features lead you to conclude that the acid is unsaturated and conjugated.
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Examine the broad absorption band around 2500-3500 cm⁻¹. This is characteristic of the O-H stretching vibration in carboxylic acids, which is typically broad due to hydrogen bonding.

Identify the sharp peak near 1700 cm⁻¹. This corresponds to the C=O stretching vibration, which is a strong indicator of the presence of a carboxylic acid functional group.

Look for the absorption band near 1600 cm⁻¹. This is indicative of C=C stretching vibrations, suggesting the presence of an alkene group, which confirms unsaturation.

Check for additional peaks near 3000 cm⁻¹. These are associated with =C-H stretching vibrations, further supporting the presence of an alkene group.

Analyze the conjugation effects. The C=O stretching frequency near 1700 cm⁻¹ is slightly lower than typical values for non-conjugated carboxylic acids, which suggests conjugation between the alkene and the carboxylic acid group.

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Key Concepts

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

Infrared Spectroscopy (IR)

Infrared spectroscopy is a technique used to identify functional groups in organic compounds by measuring the absorption of infrared light. Different bonds absorb characteristic frequencies of IR radiation, resulting in a spectrum that displays peaks corresponding to these absorptions. Understanding how to interpret these peaks is crucial for identifying the presence of specific functional groups, such as carboxylic acids.

Carboxylic Acid Functional Group

Carboxylic acids are organic compounds characterized by the presence of a carboxyl group (-COOH). In an IR spectrum, carboxylic acids typically show a broad O-H stretching absorption around 2500-3300 cm⁻¹ and a sharp C=O stretching absorption near 1700 cm⁻¹. Recognizing these peaks is essential for confirming the presence of a carboxylic acid in a compound.

Unsaturation and Conjugation

Unsaturation in organic compounds refers to the presence of double or triple bonds, which can be identified in an IR spectrum by the presence of C=C stretching vibrations typically around 1600-1680 cm⁻¹. Conjugation occurs when double bonds are separated by a single bond, leading to a stabilization of the molecule and shifts in the absorption peaks. Identifying these features helps determine the unsaturation and conjugation of the acid.

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Related Practice

Textbook Question

The IR spectrum for anisole contains two C―O stretching bands in the fingerprint region. Match the band to the bond that gives rise to it. Why are these bands so intense?

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Textbook Question

How can you distinguish the following compounds using: a. their infrared spectra?

Textbook Question

The acid-catalyzed hydrolysis of an ester results in the formation of an equal amount of carboxylic acid and alcohol.

(b) Once separated, how could you distinguish between the carboxylic acid and alcohol using IR spectroscopy?

Textbook Question

The absence of what band in the IR spectrum of the product in Figure 18.59 would be consistent with full conversion of the carboxylic acid to an acid chloride?

Textbook Question

Following a LiAlH₄ reduction, an IR spectrum suggested that the product was a mixture of the starting amide and the desired amine.

(b) Once separated, how could you distinguish between the amide and the amine using IR spectroscopy?

Textbook Question

Which shows an O–H stretch at a larger wavenumber: ethanol dissolved in carbon disulfide or an undiluted sample of ethanol?

Open Question

Answer each of the following questions based on the images below.

a) Which compounds show an intense peak ~ 1700 cm^-1?

b) Which compound shows an intense, broad peak at ~ 3400 cm^-1?

c) Which compound has a peak at ~1700 cm^-1, but no peaks at 2700 cm^-1?

d) Which compound has no signal beyond the fingerprint region?

Multiple Choice

Identify which carbonyl group will exhibit a signal at a lower wavenumber

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The IR spectrum of trans-oct-2-enoic acid is shown. Point out the spectral characteristics that allow you to tell that this is a carboxylic acid, and show which features lead you to conclude that the acid is unsaturated and conjugated.<IMAGE>

Key Concepts

Infrared Spectroscopy (IR)

Carboxylic Acid Functional Group

Unsaturation and Conjugation

Watch next

The IR spectrum of trans-oct-2-enoic acid is shown. Point out the spectral characteristics that allow you to tell that this is a carboxylic acid, and show which features lead you to conclude that the acid is unsaturated and conjugated.
<IMAGE>