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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5:47 minutes

Problem 42(5)

Textbook Question

Describe the proton-coupled ¹³C NMR spectra for compound 5 in Problem 41, indicating the relative positions of the signals.
5.

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Analyze the structure of the compound provided in the image. The molecule is 3-methylbutanal, which contains a carbonyl group (C=O), a methyl group (CH3), and a branched alkyl chain.

Identify the unique carbon environments in the molecule. There are five distinct carbons: (1) the carbonyl carbon, (2) the CH carbon attached to the methyl group, (3) the CH3 group directly attached to the CH carbon, (4) the CH3 group attached to the CH2 carbon, and (5) the CH2 carbon attached to the carbonyl group.

Consider the proton-coupled 13C NMR spectra. Each carbon will exhibit a signal based on its chemical environment. The carbonyl carbon will appear downfield due to its high deshielding effect, while the methyl and methylene carbons will appear upfield due to their relatively shielded environments.

Determine the splitting patterns for each carbon signal based on the number of hydrogens directly attached to the carbon. For example, the CH carbon will show a doublet due to coupling with one hydrogen, while the CH3 carbons will show singlets as they are not coupled to any hydrogens directly attached to them.

Arrange the relative positions of the signals in the spectrum. The carbonyl carbon will be the furthest downfield, followed by the CH carbon, the CH2 carbon, and finally the CH3 carbons, which will appear upfield.

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Key Concepts

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

Proton-Coupled 13C NMR Spectroscopy

Proton-coupled 13C NMR spectroscopy is a technique that provides information about the carbon environment in organic compounds by observing the interaction between carbon and hydrogen nuclei. In this method, the presence of protons attached to carbon atoms influences the chemical shifts of the carbon signals, allowing for a more detailed analysis of the molecular structure and connectivity.

Chemical Shift

Chemical shift in NMR spectroscopy refers to the position of a signal in the spectrum, which is influenced by the electronic environment surrounding the nucleus. In 13C NMR, different functional groups and hybridization states of carbon atoms lead to distinct chemical shifts, helping to identify the types of carbon present in a compound. For example, carbonyl carbons typically appear downfield (higher ppm) due to their deshielding effect.

Multiplicity and Integration

Multiplicity in NMR refers to the splitting of signals due to spin-spin coupling between neighboring nuclei, which provides insight into the number of adjacent protons. In 13C NMR, while the signals are generally singlets, the presence of protons can affect their intensity and position. Integration, although less common in 13C NMR, can indicate the relative number of equivalent carbon atoms contributing to a signal, aiding in the interpretation of the molecular structure.

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Related Practice

Textbook Question

How can 1,2-, 1,3-, and 1,4-dinitrobenzene be distinguished by

b. ¹³C NMR spectroscopy?

Textbook Question

Sketch the following spectra that would be obtained for 2-chloroethanol:

d. The proton-coupled ¹³C NMR spectrum.

Textbook Question

Sketch the following spectra that would be obtained for 2-chloroethanol:

c. The ¹³C NMR spectrum.

Textbook Question

Compound A, with molecular formula C₄H₉Cl, shows two signals in its ¹³C NMR spectrum. Compound B, an isomer of compound A, shows four signals, and in the proton-coupled mode, the signal farthest downfield is a doublet. Identify compounds A and B.

Textbook Question

Answer the following questions for each compound:

a. How many signals are in its ¹³C NMR spectrum?

b. Which signal is at the lowest frequency?

9. CH₂=CHBr

Textbook Question

Answer the following questions for each compound:

a. How many signals are in its ¹³C NMR spectrum? b. Which signal is at the lowest frequency?

Textbook Question

Answer the following questions for each compound:

a. How many signals are in its ¹³C NMR spectrum?

b. Which signal is at the lowest frequency?