What absorbs at 1270 cm⁻¹ in an FTIR spectrum?
A band near 1270 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 1270 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 |
|---|---|---|---|
| Methacrylate | 12 | 12 | 1.0 |
| C-O single bond | 12 | 12 | 1.0 |
| Acetate | 12 | 12 | 1.0 |
| Methoxy (OCH3) | 11 | 11 | 1.0 |
| Alkyl C-H | 7 | 7 | 1.0 |
| Amide | 7 | 7 | 1.0 |
| Lignin | 4 | 4 | 1.0 |
| Hydroxyl (O-H) | 3 | 3 | 1.0 |
| Carboxyl (COOH) | 3 | 3 | 1.0 |
| Silicon carbon | 3 | 3 | 1.0 |
| Alkene (C=C) | 2 | 2 | 1.0 |
| Aromatic ring | 2 | 2 | 1.0 |
| Secondary amine | 2 | 2 | 1.0 |
| C n single bond | 2 | 2 | 1.0 |
| Borate | 2 | 2 | 1.0 |
| Protein | 2 | 2 | 1.0 |
| Phosphate (PO4) | 2 | 2 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| Fluorine (C-F) | 1 | 1 | 1.0 |
| Oxygen heterocycle | 1 | 1 | 1.0 |
| Silicon (Si) | 1 | 1 | 1.0 |
| Aldehyde (CHO) | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Nitrogen heterocycle | 1 | 1 | 1.0 |
| N-O bond | 1 | 1 | 1.0 |
| Phenolic | 1 | 1 | 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 |
|---|---|---|---|
| plasma | 1270, 1656, 1650 | Methacrylate, Acetate | 2 |
| chitosan | 1270, 1650, 1655 | Acetate, Methacrylate, C-O single bond | 1 |
| PHB | 1270, 3440, 1724 | Methacrylate, Acetate, Methoxy (OCH3) | 1 |
| PLLA | 1270, 1182, 921 | C-O single bond, Methoxy (OCH3), 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 1270 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
“C-H vibration24) stretching vibration and asymmetric rocking 3 cm-1 C-H C-O-C and 1270 (bending vibration of and vibration24) lead to an overestimation of the absorstretching”
Braun 等 - 2006 - Infrared spectroscopic determination of lactide co DOI: 10.1021/ma061922a -
Alkyl C-H confidence 1.0
“(2006) used the ratio of 1600/1030 (carquartz overtone bands between 1800 and 2000 and the cm-1 boxylate/polysaccharide) as an index of decomposition in peat, CH deformation band between 1270 and 1460 (Fig.”
Calderon 等 - 2011 - Chemical Differences in Soil Organic Matter Fracti DOI: 10.2136/sssaj2009.0375 -
Alkyl C-H confidence 1.0
“The peak at 1270 - unit cells of PLLA/PDLLA blends are changed by addition corresponds to CH group in PLLA, PDLLA [14] and 8 A.”
El-Hadi - 2019 - Miscibility of CrystallineAmorphousCrystalline B DOI: 10.1080/03602559.2018.1455863 -
Amide confidence 1.0
“Amide III band at 1270 is contributed by”
Erahimovitch 等 - 2006 - FTIR spectroscopy examination of leukemia patients DOI: 10.1016/j.vibspec.2005.06.004 -
Amide confidence 1.0
“1451cm(cid:1)1 NAH containingcinnamonessentialoil.Theseauthorsindicatedthatthe stretching), (amide-II, bending), (CH 2 1242cm(cid:1)1 CAN NAH liquid state of oils may provide the expansion of creamed droplets bending) and (amide-III, and st”
Development of bioactive fish gelatin/chitosan nanoparticles composite films with antimicrobial properties DOI: 10.1016/j.foodchem.2015.09.004 -
Amide confidence 1.0
“bending vibrations) and amide I hydrogen bonded stretching vibrations) regions at 1270, 1544 and”
Mukherjee 等 - 2014 - Altered metabolic profile in early and late onset DOI: 10.1016/j.preghy.2013.11.005 -
Phosphate (PO4) confidence 1.0
“The formation of covalent 1270cm-1, spectra: (PO 2) band near (PO 2) band at P-O-Cu linkages is easier in the polyphosphate glasses as s 1190cm-1, P-O1100cm-1, absorption band near about than in the metaphosphate glasses.”
Shih 等 - 2003 - P-31 MAS-NMR and FTIR analyses on the structure of DOI: 10.1016/S0254-0584(03)00098-1 -
Amide confidence 1.0
“Exis- (a.u.) 0.25 cm-1 tence of Amide III band at 1270 which arises from couAbsorbance 0.2 pling of C-N stretching and N-H bending indicates existence of some proteins consisting of C, N and H.”
Singh 等 - 2010 - Spectroscopic techniques as a diagnostic tool for DOI: 10.1007/s12206-010-0524-z
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