What absorbs at 811 cm⁻¹ in an FTIR spectrum?
A band near 811 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 811 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 | 6 | 6 | 1.0 |
| Silicon-oxygen (Si-O) | 4 | 4 | 1.0 |
| Methacrylate | 4 | 4 | 1.0 |
| Acetate | 4 | 4 | 1.0 |
| Methoxy (OCH3) | 3 | 3 | 1.0 |
| C-O single bond | 3 | 3 | 1.0 |
| Nitrogen heterocycle | 2 | 2 | 1.0 |
| Carbonyl (C=O) | 2 | 2 | 1.0 |
| Siloxane (Si-O-Si) | 2 | 2 | 1.0 |
| Water (H2O) | 2 | 2 | 1.0 |
| Metal oxygen | 2 | 1 | 1.0 |
| Metal hydroxyl | 1 | 1 | 1.0 |
| Alkene (C=C) | 1 | 1 | 1.0 |
| Thiol | 1 | 1 | 1.0 |
| C-S single bond | 1 | 1 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Carboxyl (COOH) | 1 | 1 | 1.0 |
| Amide | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
Ranking reflects accumulated literature evidence, not a single fixed rule. Always confirm against your sample context.
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 811 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
-
Metal oxygen confidence 1.0
“10 a-b), peaks at 809, 811 and 812 cm-1 mixtures, MNP-PCP shifted to 814 which assigned to As-O [35].”
Enhanced arsenic (iii) adsorption from aqueous solution by magnetic pine cone biomass DOI: 10.1016/j.matchemphys.2018.09.067 -
Water (H2O) confidence 1.0
“Effect of moisture content cm-1 FTIR analysis showed that peaks at 811 and on the performance of thin wood veneer impregnated cm-1 473 were due to the symmetric stretching and with melamine-formaldehyde resin[J].”
Qin 等 - 2023 - Preparation and properties of silica solmelamine DOI: 10.1080/15685551.2022.2162280 -
Alkyl C-H confidence 1.0
“A small peak at 811.10 cm-1 appears in the biosolar spectrum only, which is indicated as out of plane bending of C-H.”
Rahmawati 等 - 2017 - The Liquid Biodiesel Extracted From Pranajiwa (Ste DOI: 10.1063/1.4978098 -
Water (H2O) confidence 1.0
“Additionally, muscovite [61,62] was identified by the peak the peak at 811 cm-1, being more visible on the inner surface and more flattened on the In addition to the peaks attributed to absorbed water [51,52], such as those in the”
Technological and Functional Approaches Applied to Miniature Vessels with Pigment Traces: Two Middle Bronze Age Case Studies from Eastern Subcarpathians of Romania DOI: 10.3390/app13042093 -
Alkyl C-H confidence 1.0
“γCH associated with the out-of-plane deformation vibrations of the C-H groups (811”
Study of the Experimental and Simulated Vibrational Spectra Together with Conformational Analysis of Thioether Cyanobiphenyl-Based Liquid Crystal Dimers DOI: 10.3390/ijms23148005 -
Alkyl C-H confidence 1.0
“The band at 811 which corresponded to the out-of-plane CH wagging vibrations, indicates carvacrol (Schulz et al.”
Lipeh 等 - 2019 - Determination of Carvacrol Content in Alaska Yello DOI: 10.1007/s001070050285 -
Alkyl C-H confidence 1.0
“Asymmetric valence vibrations, aromatic ring, as well as by absorption at 811 cm-1 due to the twisting of =CH-group from cm-1 cm-1, ν as(CH 3), are characterized by the emergence of bands at 2955 and 2873 while”
Influence of Dimethacrylate Monomer on the Polymerization Efficacy of Resin-Based Dental Cements—FTIR Analysis DOI: 10.3390/polym14020247 -
Acetate confidence 1.0
“The methacrylated product, M-CMC, also showed the characteristic FTIR vibration bands derived from the -(C=O)O ester group, and the -C-H detected at 1715 and 811 cm-1, respectively (Figure 1B).”
Melilli 等 - 2020 - DLP 3D Printing Meets Lignocellulosic Biopolymers DOI: 10.3390/polym12081655
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