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

Infrared Spectroscopy Table

Organic Chemistry

15. Analytical Techniques:IR, NMR, Mass Spect

Infrared Spectroscopy Table

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5:22 minutes

Problem 12d,e,f

Textbook Question

Predict the characteristic infrared absorptions of the functional groups in the following molecules.
(d) pent-1-yne
(e) diethylamine
(f) pentanoic acid

Verified step by step guidance

Step 1: Understand the functional groups present in each molecule. For pent-1-yne, the functional group is a terminal alkyne (-C≡C-H). For diethylamine, the functional group is a secondary amine (-NH). For pentanoic acid, the functional group is a carboxylic acid (-COOH).

Step 2: Recall the characteristic infrared (IR) absorption ranges for each functional group. Terminal alkynes typically show a sharp C≡C stretch around 2100-2260 cm⁻¹ and a C-H stretch for the terminal alkyne around 3300 cm⁻¹. Secondary amines exhibit N-H stretching vibrations around 3300-3500 cm⁻¹ (broad, often with two peaks). Carboxylic acids show a broad O-H stretch around 2500-3300 cm⁻¹ and a strong C=O stretch around 1700-1725 cm⁻¹.

Step 3: For pent-1-yne, identify the specific IR absorptions. Look for the sharp C≡C stretch in the 2100-2260 cm⁻¹ range and the terminal alkyne C-H stretch near 3300 cm⁻¹.

Step 4: For diethylamine, identify the N-H stretching vibrations. Expect a broad absorption in the 3300-3500 cm⁻¹ range, often with two peaks due to the symmetric and asymmetric stretching of the N-H bonds.

Step 5: For pentanoic acid, identify the broad O-H stretch in the 2500-3300 cm⁻¹ range and the strong C=O stretch near 1700-1725 cm⁻¹. These are characteristic of the carboxylic acid functional group.

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Key Concepts

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

Infrared Spectroscopy

Infrared spectroscopy is an analytical technique used to identify functional groups in organic compounds by measuring the absorption of infrared light. Different functional groups absorb characteristic wavelengths of infrared radiation, leading to distinct peaks in an IR spectrum. Understanding how these absorptions correlate with molecular vibrations is essential for predicting the IR spectra of given compounds.

Functional Groups

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. Common functional groups include alcohols, amines, carboxylic acids, and alkynes, each exhibiting unique IR absorption patterns. Identifying these groups in the molecules pent-1-yne, diethylamine, and pentanoic acid is crucial for predicting their IR spectra.

Vibrational Modes

Vibrational modes refer to the different ways in which the atoms in a molecule can move relative to each other, such as stretching and bending. Each type of vibration corresponds to specific energy levels, which are reflected in the IR spectrum as absorption peaks. Recognizing the vibrational modes associated with the functional groups in the given molecules helps in predicting their characteristic IR absorptions.

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Related Practice

Textbook Question

The infrared spectra for three compounds are provided. Each compound has one or more of the following functional groups: conjugated ketone, ester, amide, nitrile, and alkyne. Determine the functional group(s) in each compound, and assign the major peaks above 1600 cm^–1.

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Textbook Question

Spectra are given for three compounds. Each compound has one or more of the following functional groups: alcohol, amine, ketone, aldehyde, and carboxylic acid. Determine the functional group(s) in each compound, and assign the major peaks above 1600 cm^–1.

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Textbook Question

A common lab experiment is the dehydration of cyclohexanol to cyclohexene.

(a) Explain how you could tell from the IR spectrum whether your product was pure cyclohexene, pure cyclohexanol, or a mixture of cyclohexene and cyclohexanol. Give approximate frequencies for distinctive peaks.

(b) Explain why mass spectrometry might not be a good way to distinguish cyclohexene from cyclohexanol.

Textbook Question

Four infrared spectra are shown, corresponding to four of the following compounds. For each spectrum, determine the structure and explain how the peaks in the spectrum correspond to the structure you have chosen.

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Textbook Question

Predict the characteristic infrared absorptions of the functional groups in the following molecules.

(a) cyclohexene

(b) pentan-2-ol

Textbook Question

These five structures all have distinguishing absorptions in the IR. Match each structure with its characteristic absorption.

(a) sharp, 2254 cm^–1

(b) very broad, centered about 3330 cm^–1

(d) broad with spikes at 3367 and 3292 cm^–1

(e) strong, sharp 1717 cm^–1

Textbook Question

Three common lab experiments are shown. In each case, describe how the IR spectrum of the product would differ from that of the reactant. Give approximate frequencies for distinctive peaks in the IR spectrum of the reactant and also that of the product.

Textbook Question

Give approximate wavenumbers for the major characteristic IR absorption bands that would be given by each of the following compounds:

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Predict the characteristic infrared absorptions of the functional groups in the following molecules. (d) pent-1-yne (e) diethylamine (f) pentanoic acid

Key Concepts

Infrared Spectroscopy

Functional Groups

Vibrational Modes

Watch next

Predict the characteristic infrared absorptions of the functional groups in the following molecules.
(d) pent-1-yne
(e) diethylamine
(f) pentanoic acid