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

1H NMR:Spin-Splitting Complex Tree Diagrams

Organic Chemistry

15. Analytical Techniques:IR, NMR, Mass Spect

1H NMR:Spin-Splitting Complex Tree Diagrams

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5:19 minutes

Problem 37

Textbook Question

Using a 60-MHz spectrometer, a chemist observes the following absorption: doublet, J = 7 Hz, at δ4.00
(a) What would the chemical shift (δ) be in the 300-MHz spectrum?
(b) What would the splitting value J be in the 300-MHz spectrum?
(c) How many hertz from the TMS peak is this absorption in the 60-MHz spectrum? In the 300-MHz spectrum?

Verified step by step guidance

Step 1: Understand the relationship between chemical shift (δ) and the spectrometer frequency. The chemical shift (δ) is a dimensionless value expressed in parts per million (ppm) and is independent of the spectrometer frequency. Therefore, the δ value remains the same regardless of the spectrometer frequency.

Step 2: Recognize that the coupling constant (J) is measured in hertz (Hz) and is independent of the spectrometer frequency. This means the J value will remain the same regardless of whether the spectrometer is 60 MHz or 300 MHz.

Step 3: Calculate the distance in hertz from the TMS peak for the 60-MHz spectrum. Use the formula: distance (Hz) = δ (ppm) × spectrometer frequency (MHz). For the 60-MHz spectrum, substitute δ = 4.00 ppm and spectrometer frequency = 60 MHz into the formula.

Step 4: Calculate the distance in hertz from the TMS peak for the 300-MHz spectrum. Use the same formula: distance (Hz) = δ (ppm) × spectrometer frequency (MHz). For the 300-MHz spectrum, substitute δ = 4.00 ppm and spectrometer frequency = 300 MHz into the formula.

Step 5: Summarize the results. The chemical shift (δ) remains the same at 4.00 ppm for both spectrometers. The coupling constant (J) remains the same at 7 Hz for both spectrometers. The distance in hertz from the TMS peak will differ between the 60-MHz and 300-MHz spectrometers, as calculated in steps 3 and 4.

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Key Concepts

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

Chemical Shift

Chemical shift (δ) refers to the resonant frequency of a nucleus relative to a standard reference, typically tetramethylsilane (TMS) in NMR spectroscopy. It is measured in parts per million (ppm) and provides insight into the electronic environment surrounding the nuclei. The chemical shift can change with the frequency of the spectrometer, but the relative position remains constant, allowing for comparisons across different instruments.

J-Coupling (Spin-Spin Splitting)

J-coupling, or spin-spin splitting, occurs when nuclei interact with each other through chemical bonds, leading to the splitting of NMR signals into multiple peaks. The coupling constant (J) quantifies the interaction strength and is measured in hertz (Hz). This value remains constant regardless of the spectrometer frequency, allowing for consistent interpretation of splitting patterns across different NMR instruments.

Spectrometer Frequency

The frequency of an NMR spectrometer, measured in megahertz (MHz), affects the sensitivity and resolution of the spectra obtained. While the chemical shift values (δ) are independent of the spectrometer frequency, the absolute frequency of the resonance peaks will change. Understanding how to convert between different spectrometer frequencies is essential for accurate analysis and comparison of NMR data.

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