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

Structure Determination without Mass Spect

Organic Chemistry

15. Analytical Techniques:IR, NMR, Mass Spect

Structure Determination without Mass Spect

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4:20 minutes

Problem 51

Textbook Question

A compound of molecular formula C₈H₈O gives the IR and NMR spectra shown here. Propose a structure, and show how it is consistent with the observed absorptions.
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Verified step by step guidance

Analyze the molecular formula C8H8O. This suggests the compound has a degree of unsaturation of 5, indicating the presence of rings and/or double bonds.

Examine the IR spectrum (not shown here). Look for key absorptions such as a strong peak around 1700 cm⁻¹, which would indicate a carbonyl group (C=O), and peaks around 3000 cm⁻¹ for aromatic C-H stretching.

Interpret the NMR spectrum provided. The peaks around 7-8 ppm suggest the presence of aromatic protons, while the singlet around 2-3 ppm could indicate a methyl group attached to a carbonyl or aromatic ring.

Propose a structure consistent with the data. A likely candidate is benzaldehyde (C6H5CHO), which has an aromatic ring and an aldehyde group. The aromatic protons would account for the peaks around 7-8 ppm, and the aldehyde proton would appear as a singlet around 9-10 ppm (not visible in the provided spectrum).

Verify the structure by matching the IR and NMR data to the proposed structure. Ensure the aromatic and aldehyde functional groups are consistent with the observed absorptions.

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Key Concepts

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

Molecular Formula Interpretation

The molecular formula C8H8O indicates that the compound contains eight carbon atoms, eight hydrogen atoms, and one oxygen atom. This information is crucial for deducing the possible structure of the compound, as it provides a framework for understanding the types of functional groups and structural features that may be present.

Infrared (IR) Spectroscopy

IR spectroscopy is a technique used to identify functional groups in a molecule based on the absorption of infrared light. Different bonds absorb characteristic wavelengths, allowing chemists to infer the presence of specific functional groups, such as alcohols, carbonyls, or aromatic rings, which can guide the structural proposal of the compound.

Nuclear Magnetic Resonance (NMR) Spectroscopy

NMR spectroscopy provides detailed information about the hydrogen and carbon environments in a molecule. The chemical shifts and splitting patterns observed in the NMR spectrum can reveal the number of hydrogen atoms attached to different carbon atoms, their connectivity, and the presence of functional groups, aiding in the elucidation of the compound's structure.

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Related Practice

Open Question

Provide the structure of the unknown compound from the given information.

Formula:C₄H₁₀O IR:3200-3600 cm^-1 ¹H NMR:0.9 ppm (6H, doublet)

1.8 ppm (1H, nonatet)

2.4 ppm (1H, singlet)

3.3 ppm (2H, doublet)

Open Question

Provide the structure of the unknown compound from the given information.

Formula:C₄H₉N IR:2950 cm^-1, 3400 cm^-1 ¹H NMR:1.0 ppm (4H, triplet)

2.1 ppm (4H, triplet)

3.2 ppm (1H, singlet)

Textbook Question

Show how you would distinguish among the following three compounds

(a) using infrared spectroscopy and no other information.

(b) using proton NMR spectroscopy and no other information.

Textbook Question

When 2-chloro-2-methylbutane is treated with a variety of strong bases, the products always seem to contain two isomers (A and B) of formula C₅H₁₀. When sodium hydroxide is used as the base, isomer A predominates. When potassium tert-butoxide is used as the base, isomer B predominates. The ¹H and ¹³C NMR spectra of A and B are given below.

(a) Determine the structures of isomers A and B.

(b) Explain why A is the major product when using sodium hydroxide as the base and why B is the major product when using potassium tert-butoxide as the base.

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Textbook Question

Given the ¹H NMR spectrum and the molecular formula, suggest a structure for each molecule. [The IR spectrum suggests the presence of two C=O bonds.]

(b) <IMAGE>

Textbook Question

The spectral data below are presented in a manner similar to what you would find in a chemistry research journal. Identify the structure for each set of data.

(c) C₇H₁₄O₂ : ¹H NMR: δ 0.91 (3H, t, J = 7.0 Hz), 1.11 (6H, d, J = 7.0 Hz), 1.82 (2H, sextet), 2.40 (1H, sept, J = 7.0 Hz), 4.14 (2H, t, J = 7.1 Hz); IR (cm ⁻¹) : 1745, 1200

Textbook Question

A compound gives the following IR spectrum. Upon reaction with sodium borohydride followed by acidification, it forms the product with the ¹H NMR spectrum shown below. Identify the starting material and the product.

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Textbook Question

Shown below is the ¹H NMR spectrum of the alkyl bromide used to make the phosphonium ylide that reacts with a ketone in a Wittig reaction to form a compound with molecular formula C₁₁H₁₄. What product is obtained from the Wittig reaction?

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A compound of molecular formula C8H8O gives the IR and NMR spectra shown here. Propose a structure, and show how it is consistent with the observed absorptions. <IMAGE>

Key Concepts

Molecular Formula Interpretation

Infrared (IR) Spectroscopy

Nuclear Magnetic Resonance (NMR) Spectroscopy

Watch next

A compound of molecular formula C₈H₈O gives the IR and NMR spectra shown here. Propose a structure, and show how it is consistent with the observed absorptions.
<IMAGE>