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

NMR Practice

Organic Chemistry

15. Analytical Techniques:IR, NMR, Mass Spect

NMR Practice

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6:02 minutes

Problem 78a

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.]
(a) Important IR bands (cm ⁻ ¹) : 1728, 1708 [Note: The pKₐ of this molecule is around 10.]
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Verified step by step guidance

Examine the IR spectrum data: The presence of two C=O bonds is indicated by the IR bands at 1728 cm⁻¹ and 1708 cm⁻¹. These are characteristic of carbonyl groups, such as ketones or aldehydes.

Consider the molecular formula and the pKₐ value: A pKₐ around 10 suggests the presence of an acidic hydrogen, possibly indicating a carboxylic acid or a similar functional group.

Analyze the ¹H NMR spectrum: Look for signals that correspond to protons near the carbonyl groups. This can help identify the specific environment of the protons and provide clues about the structure.

Combine the IR and NMR data: Use the information from both spectra to hypothesize possible structures. The presence of two carbonyl groups and an acidic hydrogen suggests a dicarboxylic acid or a similar compound.

Propose a structure: Based on the spectral data and the molecular formula, suggest a structure that fits all the given information, ensuring that it accounts for the two C=O bonds and the acidic hydrogen.

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Key Concepts

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

¹H NMR Spectroscopy

¹H NMR (Proton Nuclear Magnetic Resonance) spectroscopy is a technique used to determine the structure of organic compounds by analyzing the magnetic environment of hydrogen atoms. It provides information about the number of hydrogen atoms, their chemical environment, and how they are connected within a molecule. Peaks in the spectrum correspond to different hydrogen environments, and their splitting patterns can indicate neighboring hydrogen atoms.

IR Spectroscopy and Functional Groups

Infrared (IR) spectroscopy is used to identify functional groups in a molecule by measuring the absorption of infrared light, which causes molecular vibrations. Specific absorption bands correspond to different functional groups. In this question, the presence of two C=O bonds is indicated by IR bands at 1728 and 1708 cm⁻¹, suggesting the presence of carbonyl groups, such as ketones or aldehydes, which are crucial for determining the molecular structure.

pKₐ and Acid-Base Properties

The pKₐ value of a molecule indicates the acidity of a hydrogen atom within the molecule, reflecting how easily it can donate a proton. A pKₐ around 10 suggests the presence of a moderately acidic hydrogen, often associated with functional groups like carboxylic acids or phenols. Understanding the pKₐ helps in identifying possible acidic sites in the molecule, which is essential for proposing a plausible structure.

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Acid-Base Properties of Nitrogen Heterocycles Concept 1

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Related Practice

Textbook Question

The only organic compound obtained when compound Z undergoes the following sequence of reactions gives the ¹H NMR spectrum shown. Identify compound Z.

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Textbook Question

(b) Draw the proton NMR spectrum you would expect for butan-2-one. How well do the proton chemical shifts predict the carbon chemical shifts using the "15 to 20 times as large" rule of thumb?

Textbook Question

When heated with chromic acid, compound A forms benzoic acid. Identify compound A from its ¹H NMR spectrum.

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Textbook Question

Draw the NMR spectrum expected from ethanol that has been shaken with a drop of D₂O.

Textbook Question

A small pilot plant was adding bromine across the double bond of but-2-ene to make 2,3-dibromobutane. A controller malfunction allowed the reaction temperature to rise beyond safe limits. A careful distillation of the product showed that several impurities had formed, including the one having the NMR spectra that appear below. Determine its structure, and assign the peaks to the protons in your structure.

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Textbook Question

Identify pairs of coupled protons in the compound whose COSY spectrum is shown below.

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Textbook Question

What does cross peak X in Figure 14.34 tell you?

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Textbook Question

The ¹H NMR spectrum of 2-propen-1-ol is shown here. Indicate the protons in the molecule that are responsible for each of the signals in the spectrum.

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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.] (a) Important IR bands (cm ⁻ ¹) : 1728, 1708 [Note: The pKₐ of this molecule is around 10.]<IMAGE>

Key Concepts

¹H NMR Spectroscopy

IR Spectroscopy and Functional Groups

pKₐ and Acid-Base Properties

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.]
(a) Important IR bands (cm ⁻ ¹) : 1728, 1708 [Note: The pKₐ of this molecule is around 10.]
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