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

Organic Chemistry

15. Analytical Techniques:IR, NMR, Mass Spect

Infrared Spectroscopy

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3:41 minutes

Problem 15b

Textbook Question

Choose the bond in each pair that you expect to vibrate at the higher wavenumber.
(b) C―H vs. C―O

Verified step by step guidance

Understand that the wavenumber in infrared (IR) spectroscopy is related to the frequency of vibration of a bond. The wavenumber is inversely proportional to the mass of the atoms involved and directly proportional to the bond strength.

Recall that lighter atoms and stronger bonds tend to vibrate at higher frequencies, resulting in higher wavenumbers.

Consider the atomic masses: Hydrogen (H) is lighter than Oxygen (O), so C―H bonds involve a lighter atom compared to C―O bonds.

Evaluate the bond strengths: C―H bonds are generally stronger than C―O bonds due to the higher electronegativity difference and shorter bond length.

Conclude that the C―H bond will vibrate at a higher wavenumber than the C―O bond because it involves a lighter atom and a stronger bond.

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Key Concepts

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

Bond Vibrational Frequency

Bond vibrational frequency refers to the energy required for a bond to stretch or compress during vibration. It is influenced by the mass of the atoms and the strength of the bond. Lighter atoms and stronger bonds typically vibrate at higher frequencies, resulting in higher wavenumbers in infrared spectroscopy.

Mass of Atoms

The mass of the atoms involved in a bond affects its vibrational frequency. Lighter atoms, such as hydrogen, contribute to higher vibrational frequencies compared to heavier atoms like oxygen. This is because lighter atoms can move more easily, requiring less energy to vibrate, thus increasing the wavenumber.

Bond Strength

Bond strength is a measure of how strongly two atoms are held together in a molecule. Stronger bonds, such as C-H, typically vibrate at higher frequencies than weaker bonds like C-O. This is due to the greater energy required to stretch or compress a stronger bond, leading to higher wavenumbers in spectroscopic analysis.