What absorbs at 1521 cm⁻¹ in an FTIR spectrum?
A band near 1521 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 1521 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 | 4 | 4 | 1.0 |
| N h | 3 | 3 | 1.0 |
| Alkyl C-H | 3 | 3 | 1.0 |
| Alkene (C=C) | 2 | 2 | 1.0 |
| Carboxyl (COOH) | 2 | 1 | 1.0 |
| N n bond | 1 | 1 | 1.0 |
| Protein alpha helix | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Methoxy (OCH3) | 1 | 1 | 1.0 |
| Methacrylate | 1 | 1 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| Acetate | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 0.8 |
| Nitro (NO2) | 1 | 1 | 0.7 |
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 |
|---|---|---|---|
| rGO | 1521, 2358, 2930 | Alkyl C-H, Amide, N h | 1 |
| PLA | 1521, 1650, 1073 | Alkyl C-H | 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 1521 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
“In current spectra of NMB and NNMB FAXs, phenolic compounds cm-1 including ferulic acid divided in an initial band vibration of 1521 showed a strong”
Biochemical and Structural Characterization of Ferulated Arabinoxylans Extracted from Nixtamalized and Non-Nixtamalized Maize Bran DOI: 10.3390/foods11213374 -
confidence 1.0
“deformation of the N-H peak was observed at 1521 The change in peak intensity was more so in the ZnO-based groups compared to the TiO 2-based samples;”
Structural, Physical, and Mechanical Analysis of ZnO and TiO2 Nanoparticle-Reinforced Self-Adhesive Coating Restorative Material DOI: 10.3390/ma14247507 -
Alkyl C-H confidence 1.0
“1607 (0.18) 1587 1615 (0.12) CC/CH symmetric ring stretch 1521 1526 (0.98)”
Hydrogen Bonding in Human Manganese Superoxide Dismutase Containing 3-Fluorotyrosine DOI: 10.1529/biophysj.105.060616 -
confidence 1.0
“1C) also shows sharp peak around 1521 cm-1 (N-H bending) due to presence of CHX group.31 of savlon It is clear from the above dis-”
Chhatri 等 - 2011 - Designing polysaccharide-based antibacterial bioma DOI: 10.4161/biom.1.2.19005 -
Alkene (C=C) confidence 1.0
“1521 cm-1, due to due to C=C of aromatic rings;”
Georgescu 等 - 2021 - Thermal Behavior of the Nimesulide-Salicylic Acid DOI: 10.3390/ma14247715 -
Alkyl C-H confidence 1.0
“2976 corresponds to C-H stretching vibrations, 1652 skeletal vibration), 1521 cm-1 corresponds to C-H stretching vibrations, 1652 cm-1 (C=C skeletal vibration), 1521 cm-1 (C-C cm-1 corresponds to C-H stretching vibrations, 1652 cm-1 (C=C sk”
Complex Permittivity and Electromagnetic Interference Shielding Effectiveness of OPEFB Fiber-Polylactic Acid Filled with Reduced Graphene Oxide DOI: 10.3390/ma13204602 -
Acetate confidence 1.0
“Firstly, the C-O and C O bands at 1393.92 and 1521.18cm-1 iron supplement significantly reversed the above situations inthePSCPspectrumwereshiftedto1331.62and”
A new iron supplement: The chelate of pig skin collagen peptide and Fe2+ can treat iron-deficiency anemia by modulating intestinal flora DOI: 10.3389/fnut.2022.1055725 -
Amide confidence 1.0
“Although 4A) and compared to Amide II absorption at 1521 397”
Kim 等 - 2006 - Structural changes revealed by Fourier transform i DOI: 10.2203/dose-response.003.03.008
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