What absorbs at 1091 cm⁻¹ in an FTIR spectrum?
A band near 1091 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 1091 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 | 5 | 5 | 1.0 |
| Phosphate (PO4) | 5 | 5 | 1.0 |
| C-O single bond | 4 | 4 | 1.0 |
| Silicon-oxygen (Si-O) | 4 | 4 | 1.0 |
| Methoxy (OCH3) | 3 | 3 | 1.0 |
| Methacrylate | 3 | 3 | 1.0 |
| Acetate | 3 | 3 | 1.0 |
| Ring structure | 2 | 2 | 1.0 |
| Aromatic ring | 2 | 2 | 1.0 |
| Amide | 2 | 2 | 1.0 |
| Secondary amine | 2 | 2 | 1.0 |
| C-S single bond | 1 | 1 | 1.0 |
| Chitosan | 1 | 1 | 1.0 |
| Phosphorus | 1 | 1 | 1.0 |
| Carbonate | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| C n single 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 |
|---|---|---|---|
| PET | 1091, 1408, 800 | Alkyl C-H, C-O single bond | 1 |
| Polypyrrole | 1091, 1700, 400 | Alkyl C-H | 1 |
| clay | 1091, 1736, 2855 | Silicon-oxygen (Si-O), 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 1091 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
-
Alkyl C-H confidence 1.0
“The peak at ct cm-1 1091 is due to C-H deformation vibration whereas cm-1 cm-1 the peaks at 1140 and 1354 are due to the C-N”
Thakur 和 Lokhande - 2017 - Effect of dip time on the electrochemical behavior DOI: 10.1515/epoly-2016-0160 -
Alkyl C-H confidence 1.0
“Due to C-H deformation vibration”
Dip time-dependent SILAR synthesis and electrochemical study of highly flexible PPy-Cu(OH)2 hybrid electrodes for supercapacitors DOI: 10.1007/s10008-016-3502-2 -
confidence 1.0
“A wide, high, cm-1 and intense absorption band present at 1091 might suggest the stretching vibration of (Si-O-C) and (Si-O-Si) bonds present in the silane, while the two peaks around 816”
Enhanced Coating Protection of C-Steel Using Polystyrene Clay Nanocomposite Impregnated with Inhibitors DOI: 10.3390/polym15020372 -
confidence 1.0
“4 Previous FTIR data of alkoxy SiNPs show a relatively sharp Si-O-C peak, observed 1091cm-1, at rather than the typically broad Si-O peak observed in most alkyl capped SiNPs (Shirahata et al., 2009, Holmes et al., 2001, Pettigrew et al., 20”
The effect of alkyl chain length on the level of capping of silicon nanoparticles produced by a one-pot synthesis route based on the chemical reduction of micelle DOI: 10.1007/s11051-013-1425-8 -
Phosphate (PO4) confidence 1.0
“LLM confirmed rule peak-group candidate”
Evidence for Mild Diagenesis in Archaeological Human Bones from the Fewet Necropolis (SW Libya): New Insights and Implications from ATR–FTIR Spectroscopy DOI: 10.3390/app13020687 -
Phosphate (PO4) confidence 1.0
“In the spectral domain that is usually specific to the triply degenerate asymmetric stretching mode vibration (υ3) of the (PO43-) grit is observed the presence of two important maxima is observed at around 1031 and 1091 cm-1, respectively.”
Physicochemical Characterization of Europium-Doped Hydroxyapatite Thin Films with Antifungal Activity DOI: 10.3390/coatings12030306 -
Alkyl C-H confidence 1.0
“The band at 2877 is attributed to cm-1 peak at 1091 stretching vibrations of the aliphatic C-H groups.”
Hamisu 和 Celik - 2017 - Poly(AN-co-PEGMA)hBNNaClO4 composite electrolyte DOI: 10.1515/epoly-2017-0022 -
Acetate confidence 1.0
“The peaks at 1263 cm-1 is the characteristic peak of CO-O-C, and the characteristic peak of C-O-C is at 1091 cm-1.”
Surface Modification of Carbon Microspheres with Guanidine Phosphate and Its Application as a Flame Retardant in PET DOI: 10.3390/polym12081689
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