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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3:23 minutes

Problem 46e

Textbook Question

Based on Hooke's law, choose the bond in each pair that you expect to vibrate at a higher wavenumber.
(e) C=N vs C≡N

Verified step by step guidance

Understand Hooke's Law in the context of molecular vibrations: Hooke's Law relates the vibrational frequency of a bond to the force constant (k) and the reduced mass (μ) of the atoms involved. The formula is given by:

v = \frac{1}{2 π} \sqrt \frac{k}{μ}

, where v is the vibrational frequency.

Identify the bonds in question: We have a C=N bond (a double bond) and a C≡N bond (a triple bond).

Consider the force constant (k): Triple bonds generally have a higher force constant than double bonds because they are stronger and stiffer. This means that the C≡N bond will have a higher force constant compared to the C=N bond.

Evaluate the reduced mass (μ): The reduced mass is calculated using the formula

μ = \frac{m 1 m 2}{m 1 + m 2}

, where m1 and m2 are the masses of the atoms involved. Since both bonds involve the same atoms (carbon and nitrogen), the reduced mass will be the same for both bonds.

Determine which bond vibrates at a higher wavenumber: Since the C≡N bond has a higher force constant and the same reduced mass as the C=N bond, it will vibrate at a higher wavenumber according to Hooke's Law.

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Key Concepts

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

Hooke's Law in Vibrational Spectroscopy

Hooke's Law relates the vibrational frequency of a bond to the bond strength and the masses of the atoms involved. In vibrational spectroscopy, stronger bonds and lighter atoms result in higher vibrational frequencies, which correspond to higher wavenumbers in IR spectra.

Bond Order and Strength

Bond order refers to the number of chemical bonds between a pair of atoms. A higher bond order typically indicates a stronger bond. For example, a triple bond (C≡N) is stronger than a double bond (C=N), leading to higher vibrational frequencies and wavenumbers.

Wavenumber in IR Spectroscopy

Wavenumber is a measure of frequency used in infrared spectroscopy, expressed in reciprocal centimeters (cm⁻¹). It indicates the energy of molecular vibrations; higher wavenumbers correspond to higher energy vibrations, often seen in stronger bonds like triple bonds compared to double bonds.

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