What absorbs at 2400 cm⁻¹ in an FTIR spectrum?
A band near 2400 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 2400 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 |
|---|---|---|---|
| Carbon dioxide | 4 | 4 | 1.0 |
| Water (H2O) | 3 | 3 | 1.0 |
| N h | 3 | 2 | 1.0 |
| Alkyl C-H | 3 | 2 | 1.0 |
| Nitrile | 2 | 2 | 1.0 |
| Methacrylate | 2 | 2 | 1.0 |
| Acetate | 2 | 2 | 1.0 |
| Secondary amine | 2 | 2 | 1.0 |
| Hydroxyl (O-H) | 2 | 2 | 1.0 |
| Amide | 2 | 2 | 1.0 |
| Hydrogen bond | 2 | 1 | 1.0 |
| Methoxy (OCH3) | 1 | 1 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| C=n | 1 | 1 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Carboxyl (COOH) | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Adsorbed carbon monoxide | 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 |
|---|---|---|---|
| ZnO | 2400, 1400, 3430 | Alkyl C-H | 2 |
| soil | 2400, 575, 1240 | Alkyl C-H | 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 2400 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
-
Adsorbed carbon monoxide confidence 1.0
“The deformation band of C=O at around and absorption peaks ob2400cm(cid:2)1 served ordinary between 2300 and due to adsorbed CO molecules in air are absent in our”
Mn doped ZnO nanostructured thin films prepared by ultrasonic spray pyrolysis method DOI: 10.1016/j.spmi.2012.06.023 -
Hydroxyl (O-H) confidence 1.0
“As far as the high-frequency region is concerned (i.e., for > 2400 cm-1), the shape of the OH-stretching band shows significant changes with concentration.”
Hydrating Capabilities of the Biopolymers Produced by the Marine Thermophilic Bacillus horneckiae SBP3 as Evaluated by ATR-FTIR Spectroscopy DOI: 10.3390/ma15175988 -
Alkyl C-H confidence 1.0
“No significant difference in peak location was found in the investigated spectral region, except for the narrow cm-1 cm-1(C peaks at approximately 2800 (C-H stretch), 2400 = O stretch) and the region of”
Classification and identification of Rhodobryum roseum Limpr. and its adulterants based on fourier-transform infrared spectroscopy (FTIR) and chemometrics DOI: 10.1371/journal.pone.0172359 -
Carbon dioxide confidence 1.0
“Normalized intensity is the integrated area of ing lost their labile compounds prior to sampling, as was 2200cm-1 the CO2 peak from 2400 to normalized to weight of the the case with the analysed POM having been sampled seven sample.”
Demyan 等 - 2013 - Combining a coupled FTIR-EGA system and in situ DR DOI: 10.5194/bg-10-2897-2013 -
Acetate confidence 1.0
“The deformation the samples are observably composed nanostructures that 1000cm-1, C=O band of at about and absorption peaks look like nanorods or hexagonal prisms with a diameter of 2400cm-1 observed ordinarily between 2300 and due to”
Kharroubi 等 - 2012 - Mn doping effect on the structural properties of Z DOI: 10.1088/0031-8949/86/01/015805 -
Hydrogen bond confidence 1.0
“A hydrogen-bonding stretching band 2400exhibits a broad feature with a number of subpeaks at cm-1.”
Noguchi 等 - 1999 - Structure of a histidine ligand in the photosynthe DOI: 10.1021/bi990631 -
Water (H2O) confidence 1.0
“Unlike archaeal rhodopsins, water bands were not <2400 cm-1 rhodopsin and Batho-minus-Iso spectra by use of such marker region at 77 K for bovine observed in the bands.”
Ota 等 - 2006 - Structural changes in the Schiff base region of sq DOI: 10.1021/bi051937l -
Water (H2O) confidence 1.0
“In the M <2400 cm-1, Figure 5b,c shows that at there are two water intermediate, appearance of a protonation signal of the cm-1) bands for SRII (2307 and 2215 and three water bands counterion is a common feature among rhodopsins (SRIs, cm-1”
Suzuki 等 - 2008 - Structural Changes of Salinibacter Sensory Rhodops DOI: 10.1021/bi801358b
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