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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4:05 minutes

Problem 92a

Textbook Question

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

Verified step by step guidance

First, identify the functional groups present in each compound. Compound (A) is a carboxylic acid, compound (B) is an aldehyde, and compound (C) is an ester.

Understand the characteristic IR absorption bands for each functional group. Carboxylic acids typically show a broad O-H stretch around 2500-3000 cm^{-1> and a C=O stretch near 1700 cm^{-1>. Aldehydes have a C=O stretch around 1720-1740 cm^{-1> and may show C-H stretches near 2700-2900 cm^{-1>. Esters exhibit a C=O stretch around 1735-1750 cm^{-1> and C-O stretches near 1050-1300 cm^-1>.}}}}}

Examine the IR spectrum for compound (A). Look for the broad O-H stretch and the C=O stretch, which are indicative of a carboxylic acid.

Analyze the IR spectrum for compound (B). Identify the C=O stretch and the C-H stretches that are characteristic of an aldehyde.

Review the IR spectrum for compound (C). Detect the C=O stretch and the C-O stretches, which are typical for an ester.

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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 an analytical technique used to identify functional groups in organic compounds by measuring the absorption of infrared light. Different bonds absorb characteristic wavelengths of infrared light, leading to distinct peaks in the spectrum. This allows chemists to determine the presence of specific functional groups, such as alcohols, aldehydes, and esters, based on their unique absorption patterns.

Functional Groups

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. In the context of the compounds shown, the presence of hydroxyl (-OH), aldehyde (-CHO), and ester (-COOR) groups will influence the infrared spectrum. Recognizing these groups is essential for interpreting the spectra and distinguishing between the compounds.

Characteristic Absorption Peaks

Each functional group has a characteristic absorption peak in the infrared spectrum. For example, alcohols typically show a broad O-H stretch around 3200-3600 cm⁻¹, while carbonyl groups (C=O) appear around 1700 cm⁻¹. By analyzing these peaks, one can differentiate between compounds A, B, and C based on their unique functional groups and the corresponding absorption features in their infrared spectra.

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Related Practice

Textbook Question

Identify the important bands you would expect to find in an IR spectrum for the following molecules.

(c)

Textbook Question

A carboxylic acid can be converted to an ester using the conditions shown. Explain how a comparison of an IR spectrum of the reactant(s) and product can be used to determine whether the reaction was successful or not.

Textbook Question

Under acidic conditions, alkene A can be isomerized to the more stable alkene B. How could IR spectroscopy be used to distinguish between A and B? [There are a few correct answers.]

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

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

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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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?

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