What absorbs at 1540 cm⁻¹ in an FTIR spectrum?
A band near 1540 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 1540 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 |
|---|---|---|---|
| Amide | 86 | 77 | 1.0 |
| N h | 24 | 23 | 1.0 |
| Carboxyl (COOH) | 24 | 21 | 1.0 |
| Protein | 18 | 16 | 1.0 |
| Acetate | 17 | 15 | 1.0 |
| Methacrylate | 16 | 14 | 1.0 |
| Carbonyl (C=O) | 13 | 11 | 1.0 |
| Secondary amine | 12 | 12 | 1.0 |
| Ketone | 12 | 10 | 1.0 |
| Ester | 12 | 10 | 1.0 |
| C n single bond | 8 | 8 | 1.0 |
| Aromatic ring | 7 | 7 | 1.0 |
| Ring structure | 7 | 6 | 1.0 |
| Alkene (C=C) | 6 | 5 | 1.0 |
| Alkyl C-H | 5 | 4 | 1.0 |
| Bronsted acid site | 4 | 4 | 1.0 |
| Methoxy (OCH3) | 4 | 4 | 1.0 |
| C-O single bond | 4 | 4 | 1.0 |
| N-O bond | 4 | 4 | 1.0 |
| C c single bond | 4 | 4 | 1.0 |
| Hydroxyl (O-H) | 3 | 3 | 1.0 |
| Lipid | 3 | 3 | 1.0 |
| Nitrogen heterocycle | 3 | 2 | 1.0 |
| Bromine | 2 | 2 | 1.0 |
| Lewis acid site | 2 | 2 | 1.0 |
| Methyl | 2 | 1 | 1.0 |
| Silicon (Si) | 2 | 1 | 1.0 |
| Nitro (NO2) | 2 | 1 | 0.9 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| Fatty acid | 1 | 1 | 1.0 |
| Urethane | 1 | 1 | 1.0 |
| Protein alpha helix | 1 | 1 | 1.0 |
| Carbonate | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 0.9 |
| Nucleic acid | 1 | 0 | 1.0 |
| Protein beta sheet | 1 | 0 | 1.0 |
| Chlorine | 1 | 0 | 1.0 |
| C=n | 1 | 0 | 1.0 |
| Silicon-oxygen (Si-O) | 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 |
|---|---|---|---|
| chitosan | 1540, 1650, 1655 | Amide, N h | 1 |
| cellulose | 1540, 1735, 1650 | Amide | 1 |
| hemicellulose | 1540, 1730, 897 | Amide | 1 |
| GO | 1540, 1720, 1182 | Amide, Carboxyl (COOH) | 1 |
| rGO | 1540, 2358, 2930 | Amide, N h | 1 |
| PCL | 1540, 1751, 1724 | Amide | 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 1540 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
“It is characterized by a peak that cm-1 cm-1 for the amide carbonyl group and a peak at 1540 for the appears at 1654 cm-1 (Sharma bending vibration of N-H.”
Removal of Hexavalent Chromium by Cross-Linking Chitosan and N,N’-Methylene Bis-Acrylamide DOI: 10.1007/s40710-020-00447-2 -
Amide confidence 1.0
“1656 Amide I (protein C=O stretching) 1540 Amide II (protein N-H bend, C-N stretch) bending: lipids 1452 CH 2 COO2 1392 symmetric stretching: fatty acids”
Jeronimo 等 - 2012 - Detection of Creatine in Rat Muscle by FTIR Spectr DOI: 10.1007/s10439-012-0549-9 -
Amide confidence 1.0
“The peak at 1540 represents the amide II protein band and is attributed to N-H bending caused due to stretching of cm-1 cm-1 C-N in the protein structure.”
Lymphatic filarial serum proteome profiling for identification and characterization of diagnostic biomarkers DOI: 10.1371/journal. -
N-O bond confidence 1.0
“In all of the chitin samples, there were no peaks at 1540 The absence cm-1 of bands at 1540 could be attributed to the absence of protein contaminants showing sufficient deproteinization [17,37].”
Antimicrobial Activity of Chemically and Biologically Treated Chitosan Prepared from Black Soldier Fly (Hermetia illucens) Pupal Shell Waste DOI: 10.3390/microorganisms9122417 -
Lipid confidence 1.0
“The warm-mix additives of cm-1 mix additives of H-wax type showed peak response in the wavenumbers of 686, 730, 1327, H-wax type showed peak response in the wavenumbers of 686, 730, 1327, 1540 cm-1, cm(cid:2879)(cid:2869) cm(cid:2879)(cid:2”
Analysis of the Properties of Modified Asphalt Binder by FTIR Method DOI: 10.3390/ma15165743 -
Amide confidence 1.0
“cm-1 (GP-SPF and Absorption bands for amide II at 1538 cm-1 N-H for Sat-SPF are a result of GR-SPF) and 1540 C-N bending and stretching vibrations.”
Manesa 等 - 2022 - Fabrication and Characterization of Sericin-PVA Co DOI: 10.1021/acsomega.2c00897 -
Amide confidence 1.0
“LLM confirmed rule peak-group candidate”
Composite biocompatible hydroxyapatite⠍silk fibroin coatings for medical implants obtained by Matrix Assisted Pulsed Laser Evaporation DOI: 10.1016/j.mseb.2009.10.004 -
Amide confidence 1.0
“3.4.2 Amide I/Amide II ratio Pre-proof As it was already mentioned, the position of maximum in the Amide II region (the absorption band cm-1) at 1540 does not change upon denaturation and fibrillation, both in this work and as reported by B”
Milosevic 等 - 2020 - Exploring the potential of infrared spectroscopy i DOI: 10.1016/j.saa.2019.117882
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