Textbook Question
The IR spectrum for anisole contains two C―O stretching bands in the fingerprint region. Match the band to the bond that gives rise to it. Why are these bands so intense?
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15. Analytical Techniques:IR, NMR, Mass Spect
Infrared Spectroscopy Table
Problem 36
Textbook Question
The absence of what band in the IR spectrum of the product in Figure 18.59 would be consistent with full conversion of the carboxylic acid to an acid chloride?
Verified step by step guidance1
Understand the functional groups involved: Carboxylic acids have a characteristic O-H stretch in the IR spectrum, typically appearing around 2500-3000 cm-1. Acid chlorides, on the other hand, do not have this O-H stretch.
Identify the key IR band associated with carboxylic acids: The O-H stretch is a broad band due to hydrogen bonding and is a key indicator of the presence of a carboxylic acid group.
Recognize the transformation: When a carboxylic acid is converted to an acid chloride, the O-H group is replaced by a Cl atom, eliminating the O-H stretch from the IR spectrum.
Determine the absence of the band: The absence of the broad O-H stretch band in the IR spectrum of the product would indicate that the carboxylic acid has been fully converted to an acid chloride.
Conclude the analysis: By confirming the absence of the O-H stretch, you can conclude that the conversion to an acid chloride is complete, as acid chlorides will show a C=O stretch typically around 1800 cm-1 instead.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Infrared (IR) Spectroscopy
Infrared spectroscopy is a technique used to identify functional groups in a molecule by measuring the absorption of infrared light at different wavelengths. Each functional group absorbs IR light at characteristic frequencies, producing a spectrum that can be used to deduce the presence or absence of specific bonds in a compound.
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General Features of IR Spect
Carboxylic Acid Functional Group
A carboxylic acid contains a carbonyl group (C=O) and a hydroxyl group (O-H) attached to the same carbon atom. In IR spectroscopy, carboxylic acids typically show a broad O-H stretch around 2500-3300 cm⁻¹ and a sharp C=O stretch near 1700 cm⁻¹. The presence of these bands indicates the presence of a carboxylic acid group.
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Acid Chloride Functional Group
An acid chloride is derived from a carboxylic acid by replacing the hydroxyl group with a chlorine atom. In IR spectroscopy, acid chlorides show a strong C=O stretch around 1800 cm⁻¹, but lack the broad O-H stretch seen in carboxylic acids. The absence of the O-H band in the IR spectrum indicates conversion from a carboxylic acid to an acid chloride.
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