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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6:14 minutes

Problem 57

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.

Verified step by step guidance

Analyze the molecular formula C4H9Cl: This indicates that the compound contains 4 carbons, 9 hydrogens, and 1 chlorine atom. The presence of chlorine suggests the compound is an alkyl halide.

Interpret the 13C NMR data for Compound A: The fact that Compound A shows only two signals in its 13C NMR spectrum implies that it has symmetry, reducing the number of unique carbon environments to two.

Interpret the 13C NMR data for Compound B: Compound B, being an isomer of Compound A, also has the formula C4H9Cl. However, it shows four signals in its 13C NMR spectrum, indicating that all four carbons are in unique environments, meaning it lacks symmetry.

Analyze the proton-coupled 13C NMR data for Compound B: The signal farthest downfield being a doublet suggests that one of the carbons is directly bonded to a single hydrogen atom. This is characteristic of a carbon attached to a chlorine atom (due to the electronegativity of chlorine causing deshielding) and having one hydrogen.

Propose structures for A and B: Based on the symmetry and NMR data, Compound A is likely a symmetrical alkyl chloride, such as tert-butyl chloride (2-chloro-2-methylpropane), which has two unique carbon environments. Compound B, with four unique carbon environments and a downfield doublet, is likely 1-chlorobutane, where the carbon bonded to chlorine has one hydrogen and is deshielded.

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Key Concepts

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

NMR Spectroscopy

Nuclear Magnetic Resonance (NMR) spectroscopy is a powerful analytical technique used to determine the structure of organic compounds. It provides information about the number of unique carbon environments in a molecule, as indicated by the number of signals in the 13C NMR spectrum. The position and splitting of these signals can reveal details about the molecular structure, including functional groups and connectivity.

Isomerism

Isomerism refers to the phenomenon where two or more compounds have the same molecular formula but different structural arrangements or spatial orientations. In this case, compound A and compound B are isomers of each other, meaning they share the same formula (C4H9Cl) but differ in their connectivity or arrangement of atoms, leading to distinct NMR spectral characteristics.

Signal Splitting in NMR

In NMR spectroscopy, signal splitting occurs due to the interaction between neighboring hydrogen atoms, known as spin-spin coupling. This results in the appearance of multiple peaks for a single signal, which can provide insight into the number of adjacent protons. For example, a doublet indicates that a proton is coupled to one neighboring proton, which is crucial for deducing the structure of compound B in the given question.

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