What absorbs at 765 cm⁻¹ in an FTIR spectrum?
A band near 765 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 765 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 | 3 | 1.0 |
| Aromatic ring | 3 | 3 | 1.0 |
| Metal oxygen | 2 | 2 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Amide | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| Methoxy (OCH3) | 1 | 1 | 1.0 |
| Methacrylate | 1 | 1 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| Acetate | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Silanol (Si-OH) | 1 | 1 | 1.0 |
| Siloxane (Si-O-Si) | 1 | 1 | 1.0 |
| Silicon-oxygen (Si-O) | 1 | 1 | 1.0 |
| Silicon (Si) | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| Phosphate (PO4) | 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 |
|---|---|---|---|
| copper oxide | 765, 624, 1686 | Metal oxygen, Alkyl C-H | 1 |
| copper oxide nanoparticles | 765, 624, 1317 | Metal oxygen, Alkyl C-H | 1 |
| PLA | 765, 1650, 1073 | 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 765 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
“The two behavior of air-annealed samples of copper oxide endothermic peaks at 765(cid:3)C and 905(cid:3)C were because”
Kayani 等 - 2015 - Characterization of Copper Oxide Nanoparticles Fab DOI: 10.1007/s11664-015-3867-5 -
Phosphate (PO4) confidence 1.0
“The most sen4 825 822 823 824 sitive vibrations for substitution are bands v 1-PO and v 3-PO 4, 790 791 791 789 792 785 4 stretching the symmetric and asymmetric vibration of P-O bonds 765 761 758 763 747”
Kwasniak-Kominek 等 - 2015 - Fourier transform infrared spectroscopic study of DOI: 10.1016/j.poly.2015.07.002 -
Water (H2O) confidence 1.0
“LLM confirmed rule peak-group candidate”
Li 等 - 2021 - Mechanisms of arsenate and cadmium co-immobilized DOI: 10.1016/j.cej.2021.130410 -
Silicon (Si) confidence 1.0
“Asymmetric and symmetric on cm-1 cm-1, Si-O-Si high-brightness electron source and was fitted with a Super-X Published vibrations were recorded at 1073 and 765 cm-1.55 Si-O-C Si-OH EDS (Energy Dispersive X-ray Spectroscopy) system with inte”
Magee 等 - 2023 - Silane functionalization of WS2 nanotubes for inte DOI: 10.1039/d3nr00583f -
Acetate confidence 1.0
“New peaks that emerged at ~765 as seen in cm-1 Figure 2d, and at ~1345 in Figure 2c, are from the O = C-O deformation and the C-H (HCOO-), of the formate ion confirming the incorporation of AFT into the biopolymer.”
Proton-Conducting Biopolymer Electrolytes Based on Carboxymethyl Cellulose Doped with Ammonium Formate DOI: 10.3390/polym14153019 -
Alkyl C-H confidence 1.0
“The band located at 1070 cm-1 was attributed to the organic phosphate groups and is the characteristic band of -C=O groups and the -C=O chelate stretching of amide I band was the bands in 832 cm-1 and 765 cm-1 are characteristic of -CH out-”
Biosorption of B-aflatoxins Using Biomasses Obtained from Formosa Firethorn [Pyracantha koidzumii (Hayata) Rehder] DOI: 10.3390/toxins8070218 -
Aromatic ring confidence 1.0
“group at 1277 and 1190 cm-1, the aromatic hydrogen in-plane deformation at 1155, 1215 and 1105 cm-1, and the aromatic hydrogen's out of plane bending modes occurred at 765, 860-841 cm-1 (broad band) and diphenyl ketone band at 927 cm-1.”
Mechano-Chemical Properties of Electron Beam Irradiated Polyetheretherketone DOI: 10.3390/polym14153067 -
C c single bond confidence 1.0
“LLM confirmed rule peak-group candidate”
Inhibition of Poly(ethylenediaminetetraacetic acid-diethanolamine) on Deposition of Calcium Sulfate Crystal in Simulated Industrial Water DOI: 10.3390/cryst10060544
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