What absorbs at 825 cm⁻¹ in an FTIR spectrum?
A band near 825 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 825 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 |
| Methoxy (OCH3) | 5 | 5 | 1.0 |
| Methacrylate | 5 | 5 | 1.0 |
| C-O single bond | 5 | 5 | 1.0 |
| Acetate | 5 | 5 | 1.0 |
| Aromatic ring | 4 | 4 | 1.0 |
| Ring structure | 2 | 2 | 1.0 |
| Hydroxyl (O-H) | 2 | 2 | 1.0 |
| Nitrate | 2 | 2 | 1.0 |
| Ester | 2 | 2 | 1.0 |
| Carboxyl (COOH) | 1 | 1 | 1.0 |
| C-S single bond | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| Amide | 1 | 1 | 1.0 |
| Siloxane (Si-O-Si) | 1 | 1 | 1.0 |
| Silicon-oxygen (Si-O) | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| Alkene (C=C) | 1 | 1 | 1.0 |
| Metal oxygen | 1 | 1 | 1.0 |
| Methyl | 1 | 1 | 1.0 |
| Oxygen heterocycle | 1 | 1 | 0.9 |
| Ammonium | 1 | 1 | 0.8 |
| Metal oxo | 1 | 0 | 1.0 |
| Nitro (NO2) | 1 | 0 | 0.9 |
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 |
|---|---|---|---|
| cellulose | 825, 1735, 1650 | Alkyl C-H, Methacrylate, C-O single bond | 1 |
| DNA | 825, 1712, 1660 | Methacrylate, C-O single bond, Methoxy (OCH3) | 1 |
| silica | 825, 1100, 1080 | Alkyl C-H, Methacrylate | 1 |
| alumina | 825, 460, 1000 | 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 825 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
“Fourier Transform Infrared (FTIR) spectra of the epoxidized jatropha methyl esters (EJME) showed oxirane cm-1.1H peaks (doublet) at 825 and 843 NMR confirmed the diepoxide group at 2.85 ppm and 2.98 ppm, while the 1C diepoxide signals of NM”
Derahman 等 - 2019 - EPOXIDATION OF JATROPHA METHYL ESTERS VIA ACIDIC I DOI: 10.1590/0104-6632.20190362s20180326 -
Metal oxygen confidence 1.0
“[48] recorded infrared absorption spectrum of cm-1 cm-1 crystalline V 2O and observed vibrational peaks at 825 and 1020 and assigned to 5 (V - O) and (V = O) respectively.”
Sprayed vanadium pentoxide thin films: Influence of substrate temperature and role of HNO3 on the structural, optical, morphological and electrical properties DOI: 10.1016/j.apsusc.2017.02.039 -
Alkene (C=C) confidence 1.0
“cm-1 N N-O of stretched vibration with strong two band intensity, the peak at 1324 represents C-N cm-1 group with stretched vibration of medium-weak intensity, the peak at 1117 confirms C-O A cm-1 group with stretched vibration of two bands”
Yazhiniprabha 和 Vaseeharan - 2019 - In vitro and in vivo toxicity assessment of seleni DOI: 10.1016/j.msec.2019.109763 -
Alkyl C-H confidence 1.0
“The weak band at 825 results from C-H pears at 1035 cm-1 as a result of C-O stretching in amino acids [47].”
Antibacterial Activity of the Green Synthesized Plasmonic Silver Nanoparticles with Crystalline Structure against Gram-Positive and Gram-Negative Bacteria DOI: 10.3390/nano13081327 -
confidence 1.0
“Meanwhile, the peak at 825 °C for SA75 could be related to the formation of NiAl 2O 4, which was caused by the strong interaction of Al 2O with NiO [22].”
Effect of Modified Alumina Support on the Performance of Ni-Based Catalysts for CO2 Reforming of Methane DOI: 10.3390/catal12091066 -
Hydroxyl (O-H) confidence 1.0
“Anarrow, moderately cm-1 intense peak at 825 was probably caused by phenolic compounds containing a specifically”
Bednarek 等 - 2020 - Exploring the Biochemical Origin of DNA Sequence V DOI: 10.3390/ijms21165770 -
Carbonyl (C=O) confidence 1.0
“This same band could also be partially 1,320cm-1 825cm-1 (C(cid:2)O stretching) and observed around ascribed to the presence of carbonyl compounds (esters) as a (O-C-O bending) (Nevin et al., 2008).”
Cortea 等 - 2020 - Application of Spectroscopic and Hyperspectral Ima DOI: 10.3389/fmats.2020.601339 -
confidence 1.0
“ing vibrations at 825 Raman spectra (Figure 7) This correlates with the fact that nephrite has not been show Si-O-Si symmetric stretching vibrations around”
Delgado Robles 等 - 2015 - Non-destructive in situ spectroscopic analysis of DOI: 10.1186/s40494-015-0048-z
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