What absorbs at 1321 cm⁻¹ in an FTIR spectrum?
A band near 1321 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 1321 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 |
|---|---|---|---|
| Alkyl C-H | 9 | 7 | 1.0 |
| C-O single bond | 6 | 6 | 1.0 |
| Methoxy (OCH3) | 5 | 5 | 1.0 |
| Methacrylate | 5 | 5 | 1.0 |
| Acetate | 5 | 5 | 1.0 |
| Carbonate | 2 | 2 | 1.0 |
| Secondary amine | 2 | 1 | 1.0 |
| C n single bond | 2 | 1 | 1.0 |
| Amide | 2 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Ammonium | 1 | 1 | 1.0 |
| Carboxyl (COOH) | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 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 | 1321, 1650, 1655 | Alkyl C-H, Methacrylate, C-O single bond | 1 |
| Polyethylene | 1321, 1737, 1720 | Alkyl C-H, Methacrylate, Methoxy (OCH3) | 1 |
| CuO | 1321, 453, 1000 | Methacrylate, Methoxy (OCH3), C-O single bond | 1 |
| PEG | 1321, 1650, 1342 | Alkyl C-H, Methacrylate, 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 1321 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
“LLM confirmed rule peak-group candidate”
Modification of Poplar Wood via Polyethylene Glycol Impregnation Coupled with Compression DOI: 10.3390/f13081204 -
Acetate confidence 1.0
“and C O stretching at 1321 Pandey et al.”
CMC stabilized nano silver synthesis, characterization and its antibacterial and synergistic effect with broad spectrum antibiotics DOI: 10.1016/j.carbpol.2016.11.083 -
Alkyl C-H confidence 1.0
“The small vibration peaks at ~1321 and ~1412 are due to C-H bending and O-H scissoring.”
Proton-Conducting Biopolymer Electrolytes Based on Carboxymethyl Cellulose Doped with Ammonium Formate DOI: 10.3390/polym14153019 -
Alkyl C-H confidence 1.0
“The in-plane bending band of C-H in the aromatic hydrocarbon is detectable at 1321 cm-1, and out-of-plane bending bands are at 818 and 602 cm-1.”
Synthesis of Bioactive Chlorogenic Acid-Silica Hybrid Materials via the Sol–Gel Route and Evaluation of Their Biocompatibility DOI: 10.3390/ma10070840 -
Acetate confidence 1.0
“Chitosan peaks n-C/P/D 100 ± 15.68 cm-1 were observed at 897 and 1151 (pyranose 1% cm-1 structure), 1066 (C-O stretching), 1321 n-C/P/D 1%/G 94 ± 16.45 0.05% cm-1 cm-1 (vibration of CH), 1540 (NH bending n-C/P/D 1%/G 94 ± 17.63 0.1% cm-1 of”
Hedayatyanfard 等 - 2019 - Semi-IPN Films and Electrospun Nanofibers Based on DOI: 10.22037/ijpr.2019.1100712 -
Amide confidence 1.0
“Other notable FTIR bands include 1027 (C-N stretching of amines), cm-1 cm-1 cm-1 cm-1 2916 (secondary amine), 1510 (amide II), 1230 (amide III), 1321 cm-1 (carboxylic acid), and 3423 (alcohol), all of which strongly suggest the presence”
Phytoconstituents Assisted Biofabrication of Copper Oxide Nanoparticles and Their Antiplasmodial, and Antilarval Efficacy: A Novel Approach for the Control of Parasites DOI: 10.3390/molecules27238269 -
Alkyl C-H confidence 1.0
“The characteristic doublet for the ester group located in the HEMA spectrum at 1379 and 1321 cm-1 vanishes from the polymer spectrum because, due to polymerization, CH 2= reaction and formation of aliphatic structure occur, leaving only a b”
Influence of Dimethacrylate Monomer on the Polymerization Efficacy of Resin-Based Dental Cements—FTIR Analysis DOI: 10.3390/polym14020247 -
Acetate confidence 1.0
“respectively,11 1599 detected and attributed to amide I (C=O) and amide II (N-H), and cm-1 cm-1 3.12 the band at 1381 was attributed to the distorting vibration of C-CH At 1321 was recorded cm-1 appears the peak of the C-O stretch group.”
Inclusion and release of theophylline from chitosan based microparticles DOI: 10.3906/kim-0812-29
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