What absorbs at 1261 cm⁻¹ in an FTIR spectrum?
A band near 1261 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 1261 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 |
|---|---|---|---|
| Acetate | 15 | 15 | 1.0 |
| Methoxy (OCH3) | 14 | 14 | 1.0 |
| Methacrylate | 14 | 14 | 1.0 |
| C-O single bond | 13 | 13 | 1.0 |
| Alkyl C-H | 7 | 7 | 1.0 |
| Hydroxyl (O-H) | 4 | 4 | 1.0 |
| Silicon carbon | 3 | 3 | 1.0 |
| Amide | 3 | 3 | 1.0 |
| C c single bond | 3 | 3 | 1.0 |
| Ring structure | 3 | 3 | 1.0 |
| Silicon-oxygen (Si-O) | 2 | 2 | 1.0 |
| Silicon (Si) | 2 | 2 | 1.0 |
| Secondary amine | 2 | 2 | 1.0 |
| C n single bond | 2 | 2 | 1.0 |
| Methyl | 2 | 2 | 1.0 |
| Lignin | 2 | 2 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| Thiocarbonyl | 1 | 1 | 1.0 |
| N h | 1 | 1 | 1.0 |
| Siloxane (Si-O-Si) | 1 | 1 | 1.0 |
| C=n | 1 | 1 | 1.0 |
| Borate | 1 | 1 | 1.0 |
| Phosphorus | 1 | 1 | 1.0 |
| Phosphate (PO4) | 1 | 1 | 1.0 |
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 |
|---|---|---|---|
| PLA | 1261, 1650, 1073 | Methacrylate, Acetate, Methoxy (OCH3) | 1 |
| asphalt | 1261, 1600, 1376 | Methacrylate, Acetate, Methoxy (OCH3) | 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 1261 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
-
Hydroxyl (O-H) confidence 1.0
“CR occurs at the peak of 1261 1094 1031 804.7 and 667 cm-1, cm-1 cm-1 The absorption peaks at 1261 1094 and 1031 are identified as the bending vibrations of O-H, stretching vibrations of C-O and stretching vibrations of 804.7cm-1 S=O, respe”
Liang 等 - 2017 - Thermo-stability and aging performance of modified DOI: 10.1016/j.matdes.2017.04.060 -
Phosphate (PO4) confidence 1.0
“cm-1 which According to [17], sago starch modified with STMP has a new peak at wave number 1261.38 indicates the presence of vibrations of phosphate groups.”
Rahim 等 - 2021 - Physicochemical properties of phosphate butyrate a DOI: 10.1088/1755-1315/681/1/012043 -
Borate confidence 1.0
“As shown in Table 2, the the two ranges from 1200 to 1600 and 600 to cm-1 cm-1 vibrational peak 1261 is ascribed to B-O 800 are attributed to BO groups [20].”
Fabrication, physical, thermal and optical properties of oxyfluoride glasses doped with rare earth oxides DOI: 10.1007/s10854-021-06410-7 -
C-O single bond confidence 1.0
“OH stretching vibration 1378 1375 C-O-C symmetric stretching vibration 1261,1104,1050 1284,1111,1068”
Abdulmajid 等 - 2019 - Physicochemical Studies of Tamarind Shell Tannins DOI: 10.1039/C4RA10691A -
C=n confidence 1.0
“cm-1, cm-1, at 1579.7 1442.96 1251.09 1322.80 1291.65 1261.41 stretching, and -C=N stretching.”
Design and Characterization of Baricitinib Incorporated PLA 3D Printed Pills by Fused Deposition Modeling: An Oral Pill for Treating Alopecia Areata DOI: 10.3390/polym15081825 -
Alkyl C-H confidence 1.0
“the spectra of PVRm show a very pronounced peak with a maximum of 1261 This peak is connected to the CH symmetric deformation of polydimethylsiloxane (PDMS) [23].”
Andjelic 等 - 2023 - Characterization of Different Types of Epiretinal DOI: 10.3390/ijms24054834 -
Acetate confidence 1.0
“This was also the case for the characteristic band of 1261 (C-O stretching (C-O stretching vibration) from the spectrum of hypericin on the spectrum of Fe3O4@PDA/Hyp.”
A Facile Approach for Fabrication of Core-Shell Magnetic Molecularly Imprinted Nanospheres towards Hypericin DOI: 10.3390/polym9040135 -
Amide confidence 1.0
“cm-1 The latter also shows the lack of the new amide III band at 1261 which is pronounced for the blue class (Figure 1I).”
Fourier Transform Infrared Polarization Contrast Imaging Recognizes Proteins Degradation in Lungs upon Metastasis from Breast Cancer DOI: 10.3390/cancers13020162
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