What absorbs at 665 cm⁻¹ in an FTIR spectrum?
A band near 665 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 665 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 | 3 | 3 | 1.0 |
| N h | 3 | 3 | 1.0 |
| Ring structure | 2 | 2 | 1.0 |
| Hydroxyl (O-H) | 2 | 1 | 1.0 |
| Metal oxygen | 2 | 1 | 1.0 |
| Amide | 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 |
| Carbonate | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Metalloid oxygen | 1 | 1 | 0.85 |
| Alkene (C=C) | 1 | 1 | 0.8 |
| Sulfur | 1 | 0 | 1.0 |
| Thiol | 1 | 0 | 0.9 |
Ranking reflects accumulated literature evidence, not a single authoritative rule. Always confirm against your sample context.
Possible materials
| Material | Supporting peaks | Overlapping groups | Cited sources |
|---|---|---|---|
| Chitosan | 665, 1650, 1655 | Alkyl C-H, Hydroxyl (O-H), N h | 2 |
| ZnO | 665, 1400, 3430 | Hydroxyl (O-H), Alkyl C-H | 1 |
| sodium alginate | 665, 1636, 1080 | Hydroxyl (O-H), 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 665 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
“Er3+ with increasing the concentration of ions in the glass (300-665cm-1) termediate region which is ascribed to deformation of ΔT (>100°C) as well the higher values (which are higher than other the vibrational modes of the glass network wi”
Structural and optical properties of TeO2-Li2O-ZnO-Nb2O5-Er2O3 glass system DOI: 10.1016/j.jnoncrysol.2018.08.011 -
confidence 1.0
“assigned to chain axis O(3) vibrations”
Khan 等 - 2004 - Effects of post-annealing on the infrared active p DOI: 10.1016/j.physc.2004.04.029 -
Metal oxygen confidence 1.0
“665cm-1 confirmed Zn-O stretching vibrations A broad band at (2.5% Mn-doped ZnO), 3.61eV (5% Mn-doped ZnO), and (Almehizia et al., 2021).”
Khan 等 - 2022 - Microwave-Assisted Green Synthesis of Pure and Mn- DOI: 10.3389/fmats.2021.710155 -
Alkyl C-H confidence 1.0
“The obvious peaks at 2926 and 2859 cm-1 correspond to organic compounds that cm-1 cm-1 The flattened peak at 1422 and the medium one at 665 are attributed to The flattened peak at 1422 cm-1 and the medium one at 665 cm-1 are attributed to c”
Technological and Functional Approaches Applied to Miniature Vessels with Pigment Traces: Two Middle Bronze Age Case Studies from Eastern Subcarpathians of Romania DOI: 10.3390/app13042093 -
Hydroxyl (O-H) confidence 1.0
“amide-IV al.14 et by Gonzaga The broad and strong band located 665 amide-V cm-1 between 3490 and 3256 in the FTIR spectrum is attributed to the axial stretching of the O-H and N-H”
Gonzaga 等 - 2020 - Chitosan and Agaricus brasiliensis Polysaccharides DOI: 10.21577/0103-5053.20190264 -
confidence 1.0
“The A magnification of this eV region cm-1 N-H peak observed at 665”
Gurumendi 等 - 2023 - Enhanced Chitosan Photoluminescence by Incorporati DOI: 10.1021/acsomega.2c08072 -
Ring structure confidence 1.0
“The peak at 665 is assigned to out of plane vibrations involving ring structures (Jaouadi, M'sahli & Sakli, 2009), cm-1 the peak at 894 can be attributed to the presence of b-glycosidic linkages between the monosaccharides (Reddy, Ashok, Re”
Maache 等 - 2017 - Characterization of a novel natural cellulosic fib DOI: 10.1016/j.carbpol.2017.04.096 -
Alkyl C-H confidence 1.0
“cm-1 The absorption at 1352 corresponding to the stretching,40 vibration of S=O and the presence of fucoidan Composite films sodium alginate-based elaborated cm-1 reported.41 sulfate groups at 835 was Also, the band cm-1 around 665 is attri”
Villacres 等 - 2023 - Preparation of Composite Films of Sodium Alginate- DOI: 10.21577/0103-5053.20230064
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