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

Carbon NMR

Organic Chemistry

15. Analytical Techniques:IR, NMR, Mass Spect

Carbon NMR

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Problem 66a

Textbook Question

For the molecules in Assessment 15.58, give an approximate chemical shift for each indicated carbon. [The range of correct answers is large here.].
(a)

Verified step by step guidance

Identify the type of carbon environment in the molecule. Consider factors such as hybridization (sp3, sp2, sp), the presence of electronegative atoms, and the degree of substitution.

Understand that chemical shift values in 13C NMR are influenced by the electronic environment around the carbon atom. Electronegative atoms or groups can deshield the carbon, leading to higher chemical shift values.

Consider the typical chemical shift ranges for different types of carbon environments: sp3 hybridized carbons generally appear between 0-50 ppm, sp2 hybridized carbons between 100-150 ppm, and sp hybridized carbons around 70-90 ppm.

Evaluate the effect of nearby functional groups or atoms. For example, carbons adjacent to oxygen or nitrogen atoms may experience a shift towards higher ppm values due to deshielding effects.

Estimate the chemical shift for each indicated carbon based on the identified factors and typical ranges. Remember that the range of correct answers is large, so focus on understanding the trends and influences rather than pinpointing an exact value.

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Key Concepts

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

Chemical Shift in NMR Spectroscopy

Chemical shift is a key concept in NMR spectroscopy that refers to the resonant frequency of a nucleus relative to a standard in a magnetic field. It provides information about the electronic environment surrounding a nucleus, typically measured in parts per million (ppm). Factors such as electronegativity of nearby atoms and hybridization state can influence the chemical shift, making it a useful tool for identifying functional groups and molecular structure.

Factors Affecting Carbon Chemical Shifts

The chemical shift of carbon atoms in NMR is influenced by several factors, including the electronegativity of adjacent atoms, the hybridization of the carbon atom, and the presence of electron-withdrawing or electron-donating groups. For example, carbons bonded to electronegative atoms like oxygen or nitrogen typically show downfield shifts (higher ppm values), while those in alkyl groups are usually upfield (lower ppm values).

Interpreting NMR Spectra

Interpreting NMR spectra involves analyzing the chemical shifts, signal splitting, and integration to deduce the structure of a molecule. Each unique carbon environment in a molecule will produce a distinct signal in the carbon-13 NMR spectrum. By comparing the observed chemical shifts to known reference values, one can infer the types of carbon environments present and piece together the molecular structure.

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