What absorbs at 660 cm⁻¹ in an FTIR spectrum?
A band near 660 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 660 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 | 4 | 1.0 |
| Methoxy (OCH3) | 5 | 4 | 1.0 |
| Methacrylate | 5 | 4 | 1.0 |
| C-O single bond | 5 | 4 | 1.0 |
| Acetate | 5 | 4 | 1.0 |
| Metal oxygen | 5 | 4 | 1.0 |
| Hydroxyl (O-H) | 3 | 2 | 1.0 |
| N h | 2 | 2 | 1.0 |
| Phosphate (PO4) | 2 | 1 | 1.0 |
| Amide | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| C-S single bond | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Metalloid oxygen | 1 | 1 | 1.0 |
| Nitrate | 1 | 1 | 1.0 |
| Protein beta sheet | 1 | 1 | 1.0 |
| Protein beta turn | 1 | 1 | 1.0 |
| Silicon-oxygen (Si-O) | 1 | 1 | 0.8 |
| Phosphorus | 1 | 0 | 1.0 |
| Silicon (Si) | 1 | 0 | 1.0 |
| Silicon carbon | 1 | 0 | 1.0 |
| Methyl | 1 | 0 | 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 |
|---|---|---|---|
| ZnO | 660, 1400, 3430 | Alkyl C-H, Methacrylate, C-O single bond | 1 |
| silk fibroin | 660, 1050, 1511 | Alkyl C-H, Methoxy (OCH3), Methacrylate | 1 |
| TiO2 | 660, 1700, 1093 | Alkyl C-H, Methacrylate, C-O single bond | 1 |
| PVA | 660, 1660, 2930 | Alkyl C-H, Methacrylate, C-O single bond | 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 660 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
-
Protein beta turn confidence 1.0
“wavenumber components of Amide I at about 1,690the 12 low-complexity, highly repetitive blocks, which are mainly 1,660cm-1, β-turns β-sheet assigned to vibrations of unordered and involved in the formation of the crystalline domains, domain”
Biagiotti 等 - 2022 - Electrospun Silk Fibroin Scaffolds for Tissue Rege DOI: 10.3389/fbioe.2022.833157 -
Nitrate confidence 1.0
“The main absorption peaks cm-1 of CaSO around 660 and 600 provided no 4 interferences to nitrate bands (Verma and Deb 2007).”
Choe 等 - 2010 - An Alternate Method for Fourier Transform Infrared DOI: 10.1007/s11270-009-0091-z -
Metal oxygen confidence 1.0
“In addition, the absorption band appears at wave number 660 indicated the vibration of Zr-O that influenced by the C-H and O-H bonds [17].”
Synthesis and catalytic activity of mesoporous Al-MCM-41/UiO-66 for esterification of oleic acid DOI: 10.1063/1.5082500 -
Metalloid oxygen confidence 1.0
“VibrationsofZn-Otetrahedralbond 490 488 488 488 (ZnO4) 200 400 600 800 Te-O 615 622 624 625 bending stretching vibrations units in TeO4 (cm-1) Raman shift Te-O 660 667 667 688 bending vibrations in TeO3”
Gold nanoparticles assisted surface enhanced Raman scattering and luminescence of Er3+ doped zinc–sodium tellurite glass DOI: 10.1016/j.jlumin.2014.11.032 -
Hydroxyl (O-H) confidence 1.0
“The bands at 660 are assigned to out of plane O-H bending and γ(C-C) stretching vibration and out of plane OH cmˉ1 bending respectively.”
Sathish 等 - 2013 - Nano Composite PVA-TiO2 Thin Films for OTFTs DOI: 10.4028/www.scientific.net/AMR.678.335 -
confidence 1.0
“FTIR investigation endorsed a vibration peak at 660 associated with the characteristic Ti-O-Ti bond.”
Electrospinning Process Parameters Dependent Investigation of TiO2 Nanofibers DOI: 10.1016/j.rinp.2018.08.054 -
confidence 1.0
“cm-1 the the band position of the ZnO absorption bands by Mn incorporation present study, Raman band at 660 become stronger with that the Zn-O-Zn network is perturbed by the presence of to Mn doping concentration which is similar to that of”
Vinod 等 - 2015 - Quenching and blue shift of UV emission intensity DOI: 10.1016/j.mseb.2014.10.004 -
Ring structure confidence 1.0
“The C-H in-plane deformation at 1082-1150 C-Cl stretching cm-1, cm-1 two homopolymers have C=C stretching vibration mode vibration around 650 460-540 out-of-plane cm-1, between 1400-1600 absorption band between 660 and ring deformation.”
Alakhras - 2016 - Spectroelectrochemistry of Intrinsically Conductin DOI: 10.5935/0103-5053.20150349
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