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 28

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.

Verified step by step guidance

Step 1: Analyze reaction A (Pinacol rearrangement). The reactant contains two hydroxyl (-OH) groups, which will show broad IR peaks around 3200-3600 cm⁻¹. The product is a ketone, which will exhibit a strong IR peak for the carbonyl (C=O) group around 1700 cm⁻¹. The disappearance of the -OH peak and the appearance of the C=O peak are key differences in the IR spectra.

Step 2: Analyze reaction B (Esterification of salicylic acid). The reactant contains a carboxylic acid group (-COOH), which will show a broad peak for the O-H stretch around 2500-3000 cm⁻¹ and a sharp peak for the C=O stretch around 1700 cm⁻¹. The product is an ester, which will show a C=O stretch around 1735 cm⁻¹ and a C-O stretch around 1200-1300 cm⁻¹. The disappearance of the broad O-H peak and the shift in the C=O peak are key differences.

Step 3: Analyze reaction C (Reduction of cinnamaldehyde). The reactant contains an aldehyde group (-CHO), which will show a C=O stretch around 1720 cm⁻¹ and a C-H stretch around 2700-2900 cm⁻¹. The product is an alcohol, which will show a broad O-H stretch around 3200-3600 cm⁻¹. The disappearance of the aldehyde peaks and the appearance of the O-H peak are key differences.

Step 4: For each reaction, identify the functional group transformation and correlate it with the IR spectral changes. Functional group transformations (e.g., hydroxyl to ketone, carboxylic acid to ester, aldehyde to alcohol) directly impact the IR spectrum by introducing or removing characteristic peaks.

Step 5: Approximate frequencies for distinctive peaks: Hydroxyl (-OH) stretch: 3200-3600 cm⁻¹, Carboxylic acid O-H stretch: 2500-3000 cm⁻¹, Carbonyl (C=O) stretch: 1700-1735 cm⁻¹, Ester C-O stretch: 1200-1300 cm⁻¹, Aldehyde C-H stretch: 2700-2900 cm⁻¹. Use these values to interpret the IR spectra of reactants and products in each case.

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Key Concepts

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

Infrared (IR) Spectroscopy

Infrared spectroscopy is a technique used to identify functional groups in organic compounds by measuring the absorption of infrared light at specific wavelengths. Different functional groups absorb IR radiation at characteristic frequencies, allowing chemists to deduce the molecular structure of a compound based on its IR spectrum.

Functional Group Transformations

Functional group transformations refer to the chemical reactions that convert one functional group into another. In the provided reactions, the conversion of pinacol to pinacolone and the reduction of cinnamaldehyde to cinnamyl alcohol illustrate how the presence or absence of certain functional groups affects the IR spectrum, particularly in terms of peak positions and intensities.

Characteristic IR Peaks

Characteristic IR peaks correspond to specific bond vibrations within a molecule. For example, alcohols typically show broad O-H stretching around 3200-3600 cm⁻¹, while carbonyl groups (C=O) exhibit strong peaks near 1700 cm⁻¹. Understanding these peaks helps in predicting how the IR spectrum of a product will differ from that of its reactants after a reaction.

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Related Practice

Textbook Question

Four infrared spectra are shown, corresponding to four of the following compounds. For each spectrum, determine the structure and explain how the peaks in the spectrum correspond to the structure you have chosen.

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Textbook Question

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

(d) pent-1-yne

(e) diethylamine

(f) pentanoic acid

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

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

Textbook Question

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

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:

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