What absorbs at 1256 cm⁻¹ in an FTIR spectrum?
A band near 1256 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 1256 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 |
|---|---|---|---|
| C-O single bond | 7 | 6 | 1.0 |
| Methoxy (OCH3) | 6 | 6 | 1.0 |
| Methacrylate | 6 | 6 | 1.0 |
| Acetate | 6 | 6 | 1.0 |
| Alkyl C-H | 4 | 4 | 1.0 |
| Amide | 3 | 3 | 1.0 |
| Silicon (Si) | 3 | 3 | 1.0 |
| Hydroxyl (O-H) | 3 | 3 | 1.0 |
| C n single bond | 2 | 2 | 1.0 |
| Secondary amine | 2 | 2 | 1.0 |
| Ester | 2 | 2 | 1.0 |
| Silicon-oxygen (Si-O) | 2 | 2 | 1.0 |
| N h | 1 | 1 | 1.0 |
| Silicon carbon | 1 | 1 | 1.0 |
| Siloxane (Si-O-Si) | 1 | 1 | 1.0 |
| Phosphate (PO4) | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| Carbonate | 1 | 1 | 1.0 |
| Sulfate (SO4) | 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 |
|---|---|---|---|
| PVA | 1256, 1660, 2930 | Acetate, Methacrylate, C-O single bond | 1 |
| PMMA | 1256, 1722, 1383 | Methacrylate, Acetate, Methoxy (OCH3) | 1 |
| chitosan | 1256, 1650, 1655 | Acetate, Methacrylate, C-O single bond | 1 |
| PET | 1256, 1408, 800 | Methacrylate, Acetate, Methoxy (OCH3) | 1 |
| SiO2 | 1256, 1739, 699 | Methoxy (OCH3) | 1 |
| PVC | 1256, 834, 1195 | Methoxy (OCH3), Methacrylate, Acetate | 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 1256 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
-
Carbonate confidence 1.0
“To detect isotope-edited bicarbonate bands, peak at 1256 and part of the negative peak at 1228”
Kimura 等 - 2020 - Protonation State of a Key Histidine Ligand in the DOI: 10.1021/acs.biochem.0c00810 -
Alkyl C-H confidence 1.0
“Also, we observe the characteristic bands corresponding to the stretching modes of the ethylene glycol and ester groups at ~1126 and ~1256 cm-1 the aromatic and ethylene glycol CH2 stretching mode (1658 cm-1) and the carbonyl (C=O) stretchi”
Laskarakis 等 - 2004 - A Spectroscopic Ellipsometry study of PET membrane DOI: 10.1002/masy.200450109 -
Alkyl C-H confidence 1.0
“1244cm-1, The peak at assigned to the CH-rocking vibrationofPVCinPVC-PMMAblendisobservedtohaveshiftedto 847cm-1 1256cm-1 1438, 1168, 988 and are shifted to 2874, 1734, 1460, in the PVC-PMMA-LiCF 3SO complex.”
Ramesh 等 - 2007 - FTIR studies of PVCPMMA blend based polymer elect DOI: 10.1016/j.saa.2006.06.012 -
Acetate confidence 1.0
“cm-1 deformação axial do C=O, a região de 1420 está de acordo com a deformação angular no plano C-O-H, cm-1, banda em 1256 referente à deformação axial C-O e também envolve interações com o grupo C-O-H.”
de Medeiros 等 - 2017 - Asymmetric hybrid microporous membranes influence DOI: 10.1590/S1517-707620170002.0144 -
Acetate confidence 1.0
“Formation of ether linkage was established by the presence of absorption cm-1 peak at 1256 which is attributed to C-O-C stretches.”
Synthesis of polyimides from α,αʹ-bis(3-aminophenoxy)-p-xylene: Spectroscopic, single crystal XRD and thermal studies DOI: 10.1016/j.molstruc.2018.01.098 -
Acetate confidence 1.0
“trum exhibited strong peaks at 1721 (C =O stretching), 1256 and 1122 (C-O stretch) and small bands at 1600”
Non-invasive identification of polymers in cultural heritage collections: evaluation, optimisation and application of portable FTIR (ATR and external reflectance) spectroscopy to three-dimensional polymer-based objects DOI: 10.1186/s40494-019-0336-0 -
Amide confidence 1.0
“cm-1 cm-1 cm-1 1256 (amide III vibration modes), 1163 and 1062 (C-O-C bridge stretching), cm-1 cm-1 1004 and 968 (C-O stretching vibration in secondary and primary OH groups).”
Physicochemical Properties and Functional Characteristics of Ecologically Extracted Shrimp Chitosans with Different Organic Acids during Demineralization Step DOI: 10.3390/molecules27238285 -
Phosphate (PO4) confidence 1.0
“3200 - P=O Stretching - - 1256”
Eco-Friendly Fire-Resistant Coatings Containing Dihydrogen Ammonium Phosphate Microcapsules and Tannins DOI: 10.3390/coatings11030280
Have a spectrum with this band?
Upload your FTIR spectrum and get a full interpretation report — peak assignments with literature citations, library matches, and a literature-backed analysis — in seconds.