C=O stretches near 1700 cm-1 and O-H stretches near 3300 cm-1 identify groups.
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Each functional group absorbs in a characteristic region of the infrared spectrum, and learning these ranges allows quick assignment of peaks. An alcohol O-H stretch appears as a broad band between about 3200 and 3600 cm-1, while a carboxylic acid O-H is even broader and spans roughly 2500 to 3300 cm-1. N-H stretches occur between 3300 and 3500 cm-1, and C-H stretches of alkanes appear between 2850 and 3000 cm-1. Triple bonds absorb in the 2100 to 2260 cm-1 region, and a C=O stretch appears strongly between 1650 and 1750 cm-1, with its exact position depending on the type of carbonyl. C-O stretches fall in the fingerprint area between 1000 and 1300 cm-1.
Key ideas: Work in order: broad O-H (3200 to 3600), N-H (two sharp bands for primary amines, one for secondary), C-H (below 3000 for sp3, above 3000 for sp2, about 3300 for terminal alkyne), then C=O (aldehydes 1725, ketones 1715, esters 1740, amides 1650, acid 1710). Conjugation lowers C=O by about 30 cm-1. C=C appears near 1600 to 1680.
Common mistakes and connections: Students confuse alcohol O-H (broad, rounded) with N-H (sharper, weaker) and miss that carboxylic acid O-H overlaps the C-H region. A C=O peak absence rules out carbonyls. Ring strain raises C=O frequency, with cyclopentanone near 1745. Moisture in a sample can give a false O-H peak. Links to infrared spectroscopy, functional groups and the fingerprint region.
Functional groups absorb in characteristic ranges: C-O near 1100, C=O near 1700, triple bonds near 2200, C-H near 2900 and O-H or N-H above 3200 cm-1. The interactive lesson shows this as a live animation or chart.
A ketone C=O near 1715 cm-1 and an ester C=O near 1740 cm-1 can be told apart.
C=O stretches near 1700 cm-1 and O-H stretches near 3300 cm-1 identify groups.
Characteristic IR Absorptions is a advanced topic in Analytical, Lab & Spectroscopy. It builds on beginner and intermediate topics, so review those first if needed.
Study these earlier topics in Analytical, Lab & Spectroscopy first: Colorimetry, Calibration Curve, Infrared Spectroscopy.
The next topics in Analytical, Lab & Spectroscopy are Fingerprint Region and Raman Spectroscopy.
Yes. The interactive lesson includes a self-check question on Characteristic IR Absorptions, and the Analytical, Lab & Spectroscopy quiz draws on every topic in this area.
Characteristic IR Absorptions is topic 42 of 99 in Analytical, Lab & Spectroscopy.