What absorbs at 1121 cm⁻¹ in an FTIR spectrum?
A band near 1121 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 1121 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 |
|---|---|---|---|
| Methacrylate | 5 | 5 | 1.0 |
| Acetate | 5 | 5 | 1.0 |
| Methoxy (OCH3) | 4 | 4 | 1.0 |
| C-O single bond | 4 | 4 | 1.0 |
| C c single bond | 3 | 2 | 1.0 |
| Alkyl C-H | 3 | 2 | 1.0 |
| Carboxyl (COOH) | 2 | 2 | 1.0 |
| Amide | 2 | 2 | 1.0 |
| Phosphate (PO4) | 1 | 1 | 1.0 |
| Nucleic acid | 1 | 1 | 1.0 |
| Carbonate | 1 | 1 | 1.0 |
| Lignin | 1 | 1 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| N h | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Alkene (C=C) | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Sulfate (SO4) | 1 | 1 | 0.9 |
| Aldehyde (CHO) | 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 |
|---|---|---|---|
| rGO | 1121, 2358, 2930 | Methacrylate, Acetate, C-O single bond | 1 |
| PLA | 1121, 1650, 1073 | Methacrylate, Acetate, Methoxy (OCH3) | 1 |
| cotton | 1121, 1030, 1638 | Methacrylate, Acetate, C-O single bond | 1 |
| protein | 1121, 1650, 1640 | Methacrylate, Acetate | 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 1121 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
-
C c single bond confidence 1.0
“5c highlight peaks 940 is also dominant in PC 2 in the glycated samples cm-1 cm-1 N-C-C at 1040 and therefore it could be vibrations from the formation and 1121 as contributing to the most var-”
Mcavan 等 - 2020 - Quantification of protein glycation using vibratio DOI: 10.1039/c9an02318f -
C c single bond confidence 1.0
“The 1153 band is ascribed to C-C ring asymmetric stretching cm-1 bands are due to C-O-C glycosidic link vibrations while the 1121 and 1094”
Adebajo 等 - 2006 - Raman spectroscopic investigation of acetylation o DOI: 10.1016/j.saa.2005.07.045 -
Acetate confidence 1.0
“were observed at 3348, 3319, 2945, 2833, 1558, 1449, 1394 The bands at 1121, 1092, and cm-1 972 are due to the presence of C-O stretch (primary alcohol) and =C-H bend alkenes, O-H bending as carboxylic acids.”
Enhanced Pharmaceutically Active Compounds Productivity from Streptomyces SUK 25: Optimization, Characterization, Mechanism and Techno-Economic Analysis DOI: 10.3390/molecules26092510 -
Alkyl C-H confidence 1.0
“The weak bands at 1121, 1085, cm(cid:2)1 cm(cid:2)1 1062 can be assigned to the CH twisting.”
Synthesis, crystal structure, and characterization of cyclohexylammonium tetraisothiocyanatocobaltate(II): A single-source precursor for cobalt sulfide and oxide nanostructures DOI: 10.1016/j.heliyon.2019. -
Amide confidence 1.0
“deformation bands are at 1650 (shoulder) and 1590 The C-N stretches are found at 1121 cm-1 and 1046 whereas the vibrations belonging to ethylene moieties are located at 2929, 2884, cm-1”
High iodine adsorption by polyethyleneimine impregnated nanosilica sorbents DOI: 10.1016/j.micromeso.2019.109586 -
Acetate 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 -
Aromatic ring confidence 1.0
“The bands at 1414 cm-1 and 1121 cm-1 are attributed to the occurrence of aromatic”
Phytochemical-Assisted Synthesis of Fe3O4 Nanoparticles and Evaluation of Their Catalytic Activity DOI: 10.3390/mi13122077 -
Acetate confidence 1.0
“A band at 1719 and 1632 represents cm-1 the C = O stretches, 1121 represents C-O stretches [24].”
Studies on Optimization of Sustainable Lactic Acid Production by Bacillus amyloliquefaciens from Sugarcane Molasses through Microbial Fermentation DOI: 10.3390/su14127400
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