What absorbs at 2990 cm⁻¹ in an FTIR spectrum?
A band near 2990 cm⁻¹ can point to several functional groups. Below are the most likely assignments, ranked by how much published evidence supports each — every one traceable to literature (DOI) and cross-validated against our 130,000+ reference spectra and knowledge graph.
Backed by 8 cited sources
Quick answer
A band near 2990 cm⁻¹ is usually interpreted by checking which functional groups repeatedly co-occur there in the literature, then confirming at least one or two additional peaks in the same sample. This page ranks those assignments by accumulated evidence rather than by a single fixed textbook rule.
Possible functional-group assignments
| Functional group | Supporting facts | Cited sources | Top confidence |
|---|---|---|---|
| Alkyl C-H | 13 | 13 | 1.0 |
| N h | 4 | 4 | 1.0 |
| Hydroxyl (O-H) | 2 | 2 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| Methoxy (OCH3) | 1 | 1 | 1.0 |
| Methacrylate | 1 | 1 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| Acetate | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Amide | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
Ranking reflects accumulated literature evidence, not a single fixed rule. Always confirm against your sample context.
Possible materials
| Material | Supporting peaks | Overlapping groups | Cited sources |
|---|---|---|---|
| Polyurethanes | 2990, 1740, 1728 | N h, Carbonyl (C=O), Alkyl C-H | 1 |
| PEG | 2990, 1650, 1342 | Alkyl C-H, Hydroxyl (O-H), Carbonyl (C=O) | 1 |
| copolymer | 2990, 2921, 1540 | Alkyl C-H, Hydroxyl (O-H), Carbonyl (C=O) | 1 |
Materials are shown only when the same literature pool supports this band and at least one additional characteristic peak.
Spectrum logic
This band becomes meaningful only when read with its neighboring peaks. In practice, analysts first look at the assignments above, then check whether the same sample also shows other peaks expected for the same structural motif. A lone band near 2990 cm⁻¹ is usually not enough for material identification by itself.
Real-world usage
This type of query is common in polymer identification, unknown plastic screening, QC troubleshooting, recycled-material verification, and literature-backed peak assignment review.
Common mistakes
- Treating one isolated band as proof of a material without checking at least one or two supporting peaks.
- Ignoring overlap: multiple functional groups can contribute near the same wavenumber.
- Skipping validation when additives, blends, oxidation, or contamination may distort the spectrum.
Verification advice
When ambiguity remains, validate the hypothesis with DSC, GC-MS, or TGA, especially for blends, degraded samples, and filled polymers.
Literature behind these assignments
-
confidence 1.0
“molecules.16 4+ NH The secondary peaks at 2990 and asEd The experimental absorption spectra measured at cm-1 represent the N-H bond in GaNH or NH mol3350”
Miyazaki 等 - 2005 - Properties of radio-frequency-sputter-deposited Ga DOI: 10.1063/1.1888027g -
Alkyl C-H confidence 1.0
“LLM confirmed rule peak-group candidate”
Synthesis, characterization, and crystallization behaviors of poly(D-lactic acid)-based triblock copolymer DOI: 10.1038/s41598-020-60458-9 -
Hydrogen bond confidence 1.0
“Instead, broadband is obAcceptor (DHBQ) 2990cm1, served at which is attributed to hydrogen bond formation between the two amino groups of two donor”
Alghanmi - 2019 - Synthesis, Characterization, and Biological Evalua DOI: 10.1155/2019/1743147 -
confidence 1.0
“The region between 3410 and 3200 cm-1 was ascribed to N-H stretching vibration, whereas the region between 2990 and 2840 cm-1 to C-H stretching vibration (of both soft and hard segments).”
Branched Polyurethanes Based on Synthetic Polyhydroxybutyrate with Tunable Structure and Properties DOI: 10.3390/polym10080826 -
confidence 1.0
“cm-1 cm-1 bands at 3200 and 1200-880 refer to a hydroxyl or amino group (N-H stretching C-N+ first ones and symmetric stretching second ones), meanwhile vibrational bands at 2990cm-1 cm-1 cm-1 2850 and 1485-1420 refer to an alkyl group, bei”
Delgado-Mellado 等 - 2018 - Thermal stability of choline chloride deep eutecti DOI: 10.1016/j.molliq.2018.03.076 -
Alkyl C-H confidence 1.0
“FTIR data revealed that Ery-PLGA nanoparticles' peaks were around 3650 cm-1 and 3500 cm-1 due to O-H stretching vibrations, at near 2950 cm-1 and 2990 cm-1 assigned to CH stretch vibrations, 1760 cm-1 to C=O, 1460 cm-1 attributed to C-H bin”
Nano-Architectonics of Antibiotic-Loaded Polymer Particles as Vehicles for Active Molecules DOI: 10.3390/app12041998 -
Hydroxyl (O-H) confidence 1.0
“The broad band between 3660 cm-1 and 2990 cm-1 is associated with complex vibrational stresses of free, inter-, and intramolecular bonds of hydroxyl groups [49,50].”
Morphology and Selected Properties of Modified Potato Thermoplastic Starch DOI: 10.3390/polym15071762 -
Acetate confidence 1.0
“size and morphology, which were studied from XRD, Effect of Capping Agent on the Morphology, Size and Optical Properties of In 2O Nanoparticles 261 3 Room temperature Optical Absorbance Spectra of In 2O samples capped with (a) UV-Vis absopt”
Latha 等 - 2017 - Effect of Capping Agent on the Morphology, Size an DOI: 10.1590/1980-5373-MR-2016-0292
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