What absorbs at 1800 cm⁻¹ in an FTIR spectrum?
A band near 1800 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 1800 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 |
|---|---|---|---|
| Carbonyl (C=O) | 27 | 22 | 1.0 |
| Amide | 16 | 16 | 1.0 |
| Carboxyl (COOH) | 14 | 12 | 1.0 |
| Methacrylate | 13 | 13 | 1.0 |
| Acetate | 13 | 13 | 1.0 |
| Ketone | 11 | 11 | 1.0 |
| Ester | 11 | 11 | 1.0 |
| Alkyl C-H | 10 | 9 | 1.0 |
| Hydroxyl (O-H) | 6 | 6 | 1.0 |
| Alkene (C=C) | 5 | 5 | 1.0 |
| N-O bond | 3 | 3 | 1.0 |
| Protein | 2 | 2 | 1.0 |
| Methoxy (OCH3) | 2 | 2 | 1.0 |
| C-O single bond | 2 | 2 | 1.0 |
| Secondary amine | 2 | 2 | 1.0 |
| C n single bond | 2 | 2 | 1.0 |
| Water (H2O) | 2 | 2 | 1.0 |
| Carbonate | 2 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| Adsorbed carbon monoxide | 1 | 1 | 1.0 |
| Nucleic acid | 1 | 1 | 1.0 |
| N h | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| Fatty acid | 1 | 1 | 1.0 |
| Lipid | 1 | 1 | 1.0 |
| C=n | 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 |
|---|---|---|---|
| cotton fabric | 1800, 900, 862 | Methacrylate, Amide | 1 |
| DNA | 1800, 1712, 1660 | Amide, Methacrylate, 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 1800 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
-
Hydroxyl (O-H) confidence 1.0
“1422.2 1423.5 1425.8 1425.7 1428.6 1426.9 1423.5 1428.6 Due to carbonation intensity increases 1484.6 1484.6 as hydration progresses - 1600 1673 1657.7 1657.7 1657.2 1640.3 1657.7 Due to H-O-H bending vibration 1800.3 1800 1795.2 - -”
Theoretical and experimental study of structures and properties of cement paste The nanostructural aspects of C–S–H DOI: 10.1016/j.jpcs.2011.05.001 -
Alkyl C-H confidence 1.0
“(2006) used the ratio of 1600/1030 (carquartz overtone bands between 1800 and 2000 and the cm-1 boxylate/polysaccharide) as an index of decomposition in peat, CH deformation band between 1270 and 1460 (Fig.”
Calderon 等 - 2011 - Chemical Differences in Soil Organic Matter Fracti DOI: 10.2136/sssaj2009.0375 -
Carbonyl (C=O) confidence 1.0
“LLM confirmed rule peak-group candidate”
Characterization of cotton fabric scouring by Fourier transform-infrared attenuated total reflectance spectroscopy, gas chromatography-mass spectrometry and water absorption measurements DOI: 10.1177/0040517518790976 -
Alkene (C=C) confidence 1.0
“Absorption bands in the region between 1800 and 1500 were mainly derived from the vibration of double bonds, such as C=N, C=O and C=C [21,25].”
Han 等 - 2018 - Insight into Rapid DNA-Specific Identification of DOI: 10.3390/molecules23112842 -
Alkene (C=C) confidence 1.0
“cm-1 The IR absorption bands in the region between 1800 and 1500 were mainly assigned to the C=C, C=N, and C=O stretching vibrations (Banyay et al., 2003;”
A novel FTIR discrimination based on genomic DNA for species-specific analysis of meat and bone meal DOI: 10.1016/j.foodchem.2019.05.088 -
Alkyl C-H confidence 1.0
“The spectra of goat leathers in region from 1800 to the vibrations at and at were almost absent in 2919cm(cid:3)1, 3003cm(cid:3)1 -C-H, were merged with the band at in the vegetable tanned the spectra of the chrome tanned leather.”
Hassan - 2019 - Fourier transform infrared spectroscopy to detect DOI: 10.1080/00387010.2019.1623262 -
Alkyl C-H confidence 1.0
“2917 corre3 Transmission FTIR Microscopic mode.32-34 sponded to the asymmetric CH stretching 2 Measurements cm(cid:1)1 The spectral absorption between 1800 and 1000 cm(cid:1)1 is the fingerprint region.”
Pressure dependence of human fibrinogen correlated to the conformational [alpha]-helix to [beta]-sheet transition: An Fourier transform infrared study microspectroscopic study DOI: 10.1002/bip.20012 -
Water (H2O) confidence 1.0
“and water peaks below 1800 As shown 20 21”
Powell 等 - 2017 - CO Adsorption on AuTiO2 Catalysts Observations, DOI: 10.1021/acs.jpcc.7b07249
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