Multiple Choice
Match the following functional group choices with the supplied infrared spectra data
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15. Analytical Techniques:IR, NMR, Mass Spect
IR Spect:Extra Practice
Multiple Choice
What are the characteristic bands in an IR spectrum corresponding to a carboxylic acid?
A
~ 1700 cm−1 and ~ 1050 cm−1
B
~ 1700 cm−1 and ~ 2700, 2800 cm−1
C
~ 1700 cm−1 and ~ 2400 – 3600 cm−1 (broad)
D
~ 3300 cm−1 (broad) and ~ 1050 cm−1
Verified step by step guidance1
Identify the functional group present in a carboxylic acid. A carboxylic acid contains both a carbonyl group (C=O) and a hydroxyl group (O-H).
Understand the IR spectrum characteristics of the carbonyl group. The carbonyl group typically shows a strong absorption band around 1700 cm-1 due to the C=O stretching vibration.
Recognize the IR spectrum characteristics of the hydroxyl group in carboxylic acids. The O-H group in carboxylic acids shows a broad absorption band due to hydrogen bonding, typically in the range of 2400 – 3600 cm-1.
Consider the effect of hydrogen bonding on the O-H stretch. In carboxylic acids, the O-H stretch is broader and shifted to lower frequencies compared to alcohols, due to strong hydrogen bonding.
Combine the characteristic bands for both functional groups. The IR spectrum of a carboxylic acid will show a strong band around 1700 cm-1 for the C=O stretch and a broad band in the range of 2400 – 3600 cm-1 for the O-H stretch.
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