What absorbs at 818 cm⁻¹ in an FTIR spectrum?
A band near 818 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 818 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 | 4 | 4 | 1.0 |
| Methoxy (OCH3) | 3 | 3 | 1.0 |
| Methacrylate | 3 | 3 | 1.0 |
| C-O single bond | 3 | 3 | 1.0 |
| Acetate | 3 | 3 | 1.0 |
| C c single bond | 2 | 2 | 1.0 |
| Silicon-oxygen (Si-O) | 2 | 2 | 1.0 |
| Oxygen heterocycle | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Metal hydroxyl | 1 | 1 | 1.0 |
| Nitrate | 1 | 1 | 1.0 |
| Silicon (Si) | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 0.8 |
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 |
|---|---|---|---|
| alginate | 818, 1100, 1715 | Methacrylate, Alkyl C-H, Methoxy (OCH3) | 1 |
| copper oxide | 818, 624, 1686 | Alkyl C-H, Methacrylate | 1 |
| montmorillonite | 818, 1637, 523 | Methacrylate | 1 |
| nanocomposites | 818, 1717, 1630 | Alkyl C-H, C-O single bond, Methacrylate | 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 818 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
-
confidence 1.0
“Finally, the band at cm-1 cm-1 cm-1 818 correlates with Si-O stretching, at 753 to Al-O-Si, at 699 to Si-O, and cm-1 at 616 to the coupled Al-O and Si-O [35].”
Caliman 等 - 2023 - Gellan Gum-Montmorillonite Nanocomposites for Elec DOI: 10.3390/coatings13020350 -
C c single bond confidence 1.0
“The band 818 cm-1 is assigned with the C-C 1629 cm-1 is associated with the Carbonyl (C=C) stretching of alkanes.”
Veeramani 等 - 2022 - Vitamin Aand C-rich Pouteria camito fruit derive DOI: 10.4314/ahs.v22i1.78 -
Acetate confidence 1.0
“Page 11 of 39 AUTHOR SUBMITTED MANUSCRIPT - MRX-112548.R1 Manuscript 1 2 3 amines), 1025 (C-O stretch of phenols), 818 (NH bond of amines), 761 (C-H bonded aromatic”
Yugandhar 等 - 2019 - Biofabrication, characterization and evaluation of DOI: 10.1088/2053-1591/ab0db9 -
Silicon (Si) confidence 1.0
“Finally, deconvolution in the 700 to 820 range showed three bands (see cm-1, 2): two of them, at 736 and 772 cm-1, were associated with a phonon mode of m-HfO2 [23] inset in Figure 2): two of them, at 736 and 772 were associated with a phon”
Surface Morphology and Optical Properties of Hafnium Oxide Thin Films Produced by Magnetron Sputtering DOI: 10.3390/ma16155331 -
Nitrate confidence 1.0
“1321 and out-of-plane bending bands are at 818 and 602 The spectra of the SiO 2/CGA hybrids show all the described SiO peaks, whereas it lacks nitrate signals.”
Synthesis of Bioactive Chlorogenic Acid-Silica Hybrid Materials via the Sol–Gel Route and Evaluation of Their Biocompatibility DOI: 10.3390/ma10070840 -
confidence 1.0
“Dovepress Ebadi et al cm-1 170-433 occurred in the region of °C with 97.6% weight addition, the bands at 818 and 546 are due to the Zn-OH 5-fluorouracil loss.30 vibrations of Al-OH and in the layer crystal lattice, The TGA/DTG thermograms f”
Ebadi 等 - 2019 - Synthesis and properties of magnetic nanotheranost DOI: 10.2147/IJN.S214923 -
Acetate confidence 1.0
“The absorption band at 818 was attributed to the C-O-S”
Sulfation of arabinogalactan with sulfamic acid under homogeneous conditions in dimethylsulfoxide medium DOI: 10.1007/s00226-021-01341-2 -
Alkyl C-H confidence 1.0
“Moreover, the majority cm-1 are attributed to the C-H vibration of and 818 of previous reports in literature suggest that sodium”
Lopes 等 - 2017 - Preparation and characterization of alginate and g DOI: 10.1590/0001-3765201720170071
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