What absorbs at 1140 cm⁻¹ in an FTIR spectrum?
A band near 1140 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 1140 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 | 12 | 12 | 1.0 |
| Methoxy (OCH3) | 10 | 10 | 1.0 |
| Methacrylate | 10 | 10 | 1.0 |
| Acetate | 10 | 10 | 1.0 |
| Hydroxyl (O-H) | 7 | 7 | 1.0 |
| Alkyl C-H | 7 | 7 | 1.0 |
| Aromatic ring | 7 | 6 | 1.0 |
| Secondary amine | 5 | 5 | 1.0 |
| Amide | 5 | 5 | 1.0 |
| Silicon-oxygen (Si-O) | 5 | 4 | 1.0 |
| C n single bond | 4 | 4 | 1.0 |
| N h | 4 | 4 | 1.0 |
| Carbonyl (C=O) | 3 | 3 | 1.0 |
| Silicon (Si) | 2 | 2 | 1.0 |
| Phosphate (PO4) | 2 | 2 | 1.0 |
| Siloxane (Si-O-Si) | 2 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Carboxyl (COOH) | 1 | 1 | 1.0 |
| Amine primary | 1 | 1 | 1.0 |
| Lignin | 1 | 1 | 1.0 |
| Nucleic acid | 1 | 1 | 0.9 |
| S eq o | 1 | 1 | 0.8 |
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 |
|---|---|---|---|
| polyaniline | 1140, 1565, 1570 | Methacrylate, Acetate | 2 |
| lignin | 1140, 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 1140 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
“iv) the prominent band at 1140 cm-1 is in agreement with the reported by several authors for the vibrational mode of protonated amines (-N-H+) generated during the acid doping process of the CP [35,36];”
Bongiovanni Abel 等 - 2019 - Synthesis of a Smart Conductive Block Copolymer Re DOI: 10.3390/polym11111744 -
Lignin confidence 1.0
“Relation of intensities of meters of mild isolated lignins there was cm(cid:1)1 two bands at 1140 and 1125 revealed that degradation of lignin strucchanges (cid:1) Copyright 2008 WILEY-VCH Verlag GmbH & Co.”
Derkacheva 和 Sukhov - 2008 - Investigation of lignins by FTIR spectroscopy DOI: 10.1002/masy.200850507 -
Alkyl C-H confidence 1.0
“cm-1 The band at 1140 is the result of the sum of the contribution of C-H deformation in aromatic rings cm-1 and C-O stretching in primary alcohols.”
Esteves 等 - 2013 - CHEMICAL CHANGES OF HEAT TREATED PINE AND EUCALYPT DOI: 10.4067/S0718-221X2013005000020 -
Acetate confidence 1.0
“C =O 1300-900 1235 Stretch C-O 1140”
Identification of cellulose nitrate based adhesive repairs in archaeological pottery of the University of Melbourne’s Middle Eastern archaeological pottery collection using portable FTIR-ATR spectroscopy and PCA DOI: 10.1186/s40494-016-0116-z -
Aromatic ring confidence 1.0
“Acetone is used of aromatic nuclei, assigned to the stretching of 1140cm(cid:2)1 to dissolve any unreacted aniline.”
Dielectric relaxation and ac conductivity of polyaniline⠍zinc ferrite composite DOI: 10.1016/j.compositesb.2012.01.090 -
confidence 1.0
“The characteristic absorption peaksarefoundtobeat2922cm-1isduetotheC Hstretching,1566cm-1iscorrespondsto cm-1 cm-1 C stretching vibration of quinoid ring, 1548 for C N bond stretching, 1494 C cm-1 is corresponds to stretching vibration of b”
Patil 等 - 2011 - Electrical Conductivity of PolyanilineNiZnO3 Comp DOI: 10.1080/00150193.2011.620836 -
Acetate confidence 1.0
“The normalized ofPtBMA,wecarriedoutdensityfunctionaltheory(DFT)calculations using the nonlocal density function of Becke's three parameters C-O cm-1 intensities of the stretching bands in the 1140 employingtheLee-Yang-Parrfunctional(B3LYP)w”
Shin 等 - 2002 - Structural comparison of Langmuir-Blodgett and spi DOI: 10.1021/la020135d -
Alkyl C-H confidence 1.0
“The peak at ct cm-1 1091 is due to C-H deformation vibration whereas cm-1 cm-1 the peaks at 1140 and 1354 are due to the C-N”
Thakur 和 Lokhande - 2017 - Effect of dip time on the electrochemical behavior DOI: 10.1515/epoly-2016-0160
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