What absorbs at 820 cm⁻¹ in an FTIR spectrum?
A band near 820 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 820 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 | 9 | 7 | 1.0 |
| Methoxy (OCH3) | 5 | 5 | 1.0 |
| Methacrylate | 5 | 5 | 1.0 |
| Acetate | 5 | 5 | 1.0 |
| C-O single bond | 4 | 4 | 1.0 |
| Aromatic ring | 4 | 3 | 1.0 |
| Silicon carbon | 3 | 3 | 1.0 |
| Oxygen heterocycle | 3 | 3 | 1.0 |
| Phosphate (PO4) | 3 | 2 | 1.0 |
| Ring structure | 3 | 2 | 1.0 |
| Silicon-oxygen (Si-O) | 2 | 2 | 1.0 |
| Silicon (Si) | 2 | 2 | 1.0 |
| Secondary amine | 2 | 2 | 1.0 |
| Sulfate (SO4) | 2 | 2 | 1.0 |
| Phosphorus | 2 | 1 | 1.0 |
| N h | 2 | 1 | 1.0 |
| Hydroxyl (O-H) | 2 | 1 | 1.0 |
| C c single bond | 2 | 1 | 1.0 |
| N-O bond | 1 | 1 | 1.0 |
| Methyl | 1 | 1 | 1.0 |
| Siloxane (Si-O-Si) | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Amide | 1 | 1 | 1.0 |
| Alkene (C=C) | 1 | 0 | 1.0 |
| Metal oxygen | 1 | 0 | 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 820 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
-
Sulfate (SO4) confidence 1.0
“turbinarioides (ST) 820cm-1 was related to the sulfate at the axial C-4”
Artemisia 等 - 2019 - The Properties of Brown Marine Algae Sargassum tur DOI: 10.14499/indonesianjpharm30iss1pp43 -
Silicon (Si) confidence 1.0
“The spectra exhibit transmission peaks at around 820, 1060 and 1270 corresponding to Si-O bending, Si-O and Si-CH stretching, respectively [4].”
Chabane 等 - 2009 - Characterization of SiOF thin films deposited by P DOI: 10.4028/www.scientific.net/MSF.609.59 -
C c single bond confidence 1.0
“1254 1090 1329 cm(cid:0) 1 C-O corresponds to the stretch while the 820 band is attributed to C-C the stretch vibration [25,33,34].”
Preparation of polyvinyl alcohol hydrogel containing bacteriophage and its evaluation for potential use in the healing of skin wounds DOI: 10.1016/j.jddst.2021.102484 -
Phosphate (PO4) confidence 1.0
“These results indicate a greater tendency We note that in the ATR-FTIR spectra two sharp bands at 800840cm(cid:3)1 togeneratetherequiredvacanciesathighpH.Besides,theenergies are clearly observed, very likely due to P-O stretching H 820cm(ci”
Quantum chemical study on surface complex structures of phosphate on gibbsite DOI: 10.1016/j.saa.2015.03.013 -
Amide confidence 1.0
“The cm-1 peaks at 820, 1018, and 1104 remain stable and most C-N+ likely are related to the stretching modes of the bound headgroup.”
Nikoobakht 和 El-Sayed - 2001 - Evidence for bilayer assembly of cationic surfacta DOI: 10.1021/la010530o -
Oxygen heterocycle confidence 1.0
“The FTIR peaks of HYOOA indicate the disappearance of the absorption band at 820 13C 1H which belongs to the oxirane ring.”
Salimon 等 - 2013 - Synthesis and optimization ring opening of monoepo DOI: 10.1186/2193-1801-2-429 -
Silicon carbon confidence 1.0
“However, we observed the SiC stretching vibration at 820cm-1 875 due to contaminating oxygen attached to SiC.These shifts in the vibrational band towards the”
Swain - 2022 - Process Dependent Strain Behaviour, Fractal Analys DOI: 10.21203/rs.3.rs-374154/v1 -
Oxygen heterocycle confidence 1.0
“Peak of an epoxy group at 820 cm-1”
Polyesters Based on Linoleic Acid for Biolubricant Basestocks: Low-Temperature, Tribological and Rheological Properties DOI: 10.1371/journal.pone.0151603
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