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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5:23 minutes

Problem 30e,f

Textbook Question

For each of the following pairs of compounds, name one absorption band that can be used to distinguish between them.
e.
f.

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Identify the functional groups present in each compound in the pair. Functional groups often have characteristic absorption bands in an IR spectrum.

Consult an IR spectroscopy table to determine the wavenumber ranges for the characteristic absorption bands of the functional groups identified in each compound.

Compare the functional groups in the two compounds. Look for a functional group that is present in one compound but absent in the other. This will help you identify a distinguishing absorption band.

For the compound with the unique functional group, note the specific wavenumber range where its characteristic absorption band appears. For example, a carbonyl group (C=O) typically absorbs around 1700 cm⁻¹, while an alcohol (O-H) shows a broad band around 3200-3600 cm⁻¹.

State the absorption band (wavenumber range) that can be used to distinguish between the two compounds based on the presence or absence of the functional group.

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Key Concepts

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

Infrared Spectroscopy

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, leading to distinct absorption bands in the spectrum. Understanding how to interpret these bands is crucial for distinguishing between compounds based on their functional groups.

Functional Groups

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. Common functional groups include hydroxyl (-OH), carbonyl (C=O), and carboxyl (-COOH). Identifying these groups helps in predicting the behavior of compounds and is essential for recognizing differences between similar molecules.

Absorption Bands

Absorption bands in an IR spectrum correspond to the specific wavelengths at which a compound absorbs infrared light due to vibrational transitions of its molecular bonds. Each type of bond and functional group has a unique absorption band, allowing chemists to differentiate between compounds. Recognizing these bands is key to analyzing and interpreting IR spectra effectively.

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Related Practice

Textbook Question

Predict the characteristic infrared absorptions of the functional groups in the following molecules.

(a) cyclohexene

(b) pentan-2-ol

Textbook Question

These five structures all have distinguishing absorptions in the IR. Match each structure with its characteristic absorption.

(a) sharp, 2254 cm^–1

(b) very broad, centered about 3330 cm^–1

(d) broad with spikes at 3367 and 3292 cm^–1

(e) strong, sharp 1717 cm^–1

Textbook Question

Three common lab experiments are shown. In each case, describe how the IR spectrum of the product would differ from that of the reactant. Give approximate frequencies for distinctive peaks in the IR spectrum of the reactant and also that of the product.

Textbook Question

Give approximate wavenumbers for the major characteristic IR absorption bands that would be given by each of the following compounds:

Textbook Question

Norlutin and Enovid are ketones that suppress ovulation, so they have been used clinically as contraceptives. For which of these compounds would you expect the infrared carbonyl absorption (C=O stretch) to be at a higher frequency? Explain.

Textbook Question

Give approximate wavenumbers for the major characteristic IR absorption bands that would be given by each of the following compounds:

Textbook Question

Rank the following compounds from highest wavenumber to lowest wavenumber for their C-O absorption band:

Textbook Question

Rank the following compounds from highest wavenumber to lowest wavenumber for their C=O absorption band:

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For each of the following pairs of compounds, name one absorption band that can be used to distinguish between them. e. f.

Key Concepts

Infrared Spectroscopy

Functional Groups

Absorption Bands

Watch next

For each of the following pairs of compounds, name one absorption band that can be used to distinguish between them.
e.
f.