What absorbs at 1235 cm⁻¹ in an FTIR spectrum?
A band near 1235 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 1235 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 | 13 | 13 | 1.0 |
| Amide | 13 | 12 | 1.0 |
| Methacrylate | 12 | 12 | 1.0 |
| C-O single bond | 11 | 11 | 1.0 |
| Methoxy (OCH3) | 10 | 10 | 1.0 |
| Secondary amine | 8 | 8 | 1.0 |
| Ester | 7 | 7 | 1.0 |
| Alkyl C-H | 5 | 5 | 1.0 |
| C n single bond | 5 | 5 | 1.0 |
| N h | 5 | 4 | 1.0 |
| Lignin | 4 | 4 | 1.0 |
| Carbohydrate | 4 | 4 | 1.0 |
| Carboxyl (COOH) | 3 | 3 | 1.0 |
| Carbonyl (C=O) | 3 | 3 | 1.0 |
| Phosphate (PO4) | 3 | 3 | 1.0 |
| Nucleic acid | 3 | 3 | 1.0 |
| Ketone | 2 | 2 | 1.0 |
| Protein | 2 | 2 | 1.0 |
| S eq o | 2 | 2 | 1.0 |
| Aromatic ring | 2 | 2 | 1.0 |
| C-S single bond | 1 | 1 | 1.0 |
| Phospholipid | 1 | 1 | 1.0 |
| Phosphorus | 1 | 1 | 1.0 |
| Alkene (C=C) | 1 | 1 | 1.0 |
| Protein random coil | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| Sulfate (SO4) | 1 | 1 | 1.0 |
| Methyl | 1 | 1 | 1.0 |
| S s | 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 |
|---|---|---|---|
| polyurethanes | 1235, 1740, 1728 | Amide, Methacrylate, Acetate | 1 |
| lignin | 1235, 1035, 1510 | Methacrylate, Acetate, 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 1235 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
“The measuring area was focused on methyl bending and bands at 1235 and are different with the help of microscopy in transmission mode.”
Font 等 - 2007 - Fourier transform infrared spectroscopy as a suita DOI: 10.1016/j.aca.2007.07.021 -
Aromatic ring confidence 1.0
“cm-1 another peaks at ~ 1235 and 1364 The 1235 could be associated with out of cm-1 plane aromatic C-H bending mode and that of ~ 1364 could be associated with C-H cm-1 deformation.”
Gupta 和 Rahini - 2017 - Electrochemical synthesis and characterization of DOI: 10.1016/j.electacta.2017.10.079 -
Amide confidence 1.0
“cm-1 cm-1 650-4000 The bands at 1235 and 1290 were attributed to the C-N+ stretching vibration of polaron structure and delocalisation of π electrons respectively.2 along the PAni backbone, The presence of emeraldine salt state cm-1”
Mustapa 等 - 2018 - Fabrication of Polyaniline Based Chemical Sensor f DOI: 10.21315/jps2018.29.s1.2 -
S eq o confidence 1.0
“cm1 The sharp and distinct band appearing at 1235 is Moreover, all tested samples showed crystallization of attributed to covalent S=O within RSO 3X groups, the hard segments between 120 °C and 150 °C and melting at cm1 peaks at about”
Analysis of silver nanoparticles produced by chemical reduction of silver salt solution DOI: 10.5755/j01.ms.22.4.12503 -
Nucleic acid confidence 1.0
“Explicit assignment: 'DNA bands regions at ... 1235'”
Boydston-White 等 - 2006 - Cell-cycle-dependent variations in FTIR micro-spec DOI: 10.1016/j.bbamem.2006.04.018. -
Lignin confidence 1.0
“(0 hours) compared to the raw biomass, whereas longer processing times resulted in the cm-1, cm-1, cm-1, cm-1, disappearance of the bands at 1235 1465 1510 and 1740 assigned to lignin cm-1, and hemicellulose, and in the shrinkage of the ban”
Brienza 等 - 2022 - Unleashing lignin potential through the dithionite DOI: 10.1016/j.biortech.2018.06.004. -
Acetate confidence 1.0
“cm-1 The band around 1235 is likely from a -C-O vibration, and based on its position cm-1 and relative intensity towards the 1675 and 1545 bands, its origin is probably peptidic (amide III band) [31].”
Production of Exopolysaccharides by Cultivation of Halotolerant Bacillus atrophaeus BU4 in Glucose- and Xylose-Based Synthetic Media and in Hydrolysates of Quinoa Stalks DOI: 10.3390/fermentation8020079 -
Aromatic ring confidence 1.0
“On the other hand, the Ar-O-Ar stretching is observed at 1235 cm-1 and corresponds to aromatic.”
Functionalized KIT-6/Polysulfone Mixed Matrix Membranes for Enhanced CO2/CH4 Gas Separation DOI: 10.3390/polym12102312
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