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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5:34 minutes

Problem 55

Textbook Question

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

Verified step by step guidance

Step 1: Understand the concept of C=O absorption band in IR spectroscopy. The wavenumber of the C=O stretch depends on factors such as conjugation, inductive effects, and hydrogen bonding. Higher wavenumbers correspond to stronger bonds or less conjugation.

Step 2: Analyze the structures provided. The first compound is a ketone with two alkyl groups attached to the carbonyl carbon. The second compound is an aldehyde with one alkyl group and one hydrogen attached to the carbonyl carbon. The third compound is formaldehyde, with two hydrogens attached to the carbonyl carbon.

Step 3: Consider the inductive effects. Alkyl groups donate electron density to the carbonyl group, weakening the C=O bond and lowering the wavenumber. Hydrogen atoms do not have this electron-donating effect, so formaldehyde will have the highest wavenumber.

Step 4: Rank the compounds based on conjugation and inductive effects. Formaldehyde (third compound) has the highest wavenumber due to the absence of electron-donating alkyl groups. The aldehyde (second compound) has a lower wavenumber than formaldehyde but higher than the ketone (first compound), which has two electron-donating alkyl groups.

Step 5: Final ranking from highest wavenumber to lowest wavenumber: Formaldehyde > Aldehyde > Ketone.

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Key Concepts

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

C=O Stretching Frequency

The C=O bond exhibits a characteristic stretching frequency that can be measured in wavenumbers (cm⁻¹). This frequency is influenced by the nature of the surrounding atoms and groups, with stronger bonds and less steric hindrance typically resulting in higher wavenumbers. In general, carbonyl compounds with electron-withdrawing groups show higher wavenumber absorption due to increased bond strength.

Inductive Effect

The inductive effect refers to the electron-withdrawing or electron-donating influence of substituents on a molecule. Electron-withdrawing groups, such as halogens or carbonyls, increase the positive character of the carbonyl carbon, leading to a stronger C=O bond and thus a higher wavenumber in IR spectroscopy. Conversely, electron-donating groups can lower the wavenumber by weakening the C=O bond.

Steric Hindrance

Steric hindrance occurs when bulky groups around a reactive site impede the approach of other molecules or groups. In the context of carbonyl compounds, increased steric hindrance can lower the frequency of the C=O stretching vibration due to the reduced ability of the bond to stretch freely. This effect is particularly relevant when comparing carbonyls with different substituents, as larger groups can lead to lower wavenumber absorptions.

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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:

Textbook Question

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

Textbook Question

How can IR spectroscopy distinguish between 1-hexyne, 2-hexyne, and 3-hexyne?

Textbook Question

a. How could you use IR spectroscopy to determine whether the following reaction had occurred?

b. After purifying the product, how could you determine whether all the NH₂NH₂ had been removed?

Textbook Question

For each of the following pairs of compounds, identify one IR absorption band that could be used to distinguish between them:

Textbook Question

For each of the following pairs of compounds, identify one IR absorption band that could be used to distinguish between them:

c. CH₃CH₂CH₂OH and CH₃CH₂OCH₃

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