What absorbs at 1333 cm⁻¹ in an FTIR spectrum?
A band near 1333 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 1333 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 | 4 | 4 | 1.0 |
| N eq o | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Methyl | 1 | 1 | 1.0 |
| Methoxy (OCH3) | 1 | 1 | 1.0 |
| Methacrylate | 1 | 1 | 1.0 |
| Acetate | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Carbohydrate | 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 |
|---|---|---|---|
| PMMA | 1333, 1722, 1383 | Alkyl C-H | 1 |
| cellulose | 1333, 1735, 1650 | Alkyl C-H, Hydroxyl (O-H) | 1 |
| hemicellulose | 1333, 1730, 897 | Alkyl C-H, Hydroxyl (O-H) | 1 |
| SiO2 | 1333, 1739, 699 | Alkyl C-H, Hydroxyl (O-H) | 1 |
| polyurethane | 1333, 2270, 1700 | Alkyl C-H | 1 |
| AgNPs | 1333, 1232, 1048 | Alkyl C-H, Hydroxyl (O-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 1333 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
“The band at 1333 represents the contributions of all structural components of wood because it corresponds to C-H bending of polysaccharides which joins the cm-1”
Esteves 等 - 2013 - CHEMICAL CHANGES OF HEAT TREATED PINE AND EUCALYPT DOI: 10.4067/S0718-221X2013005000020 -
Hydrogen bond confidence 1.0
“Bending and deformation modes of carbon-hydrogen Lattice strain, particle of the order of 2 bonding also produce absorption peaks in the one-phonon size, impurity inclusion, etc., cause broadening and shifting cm(cid:50)1).10 ((cid:44)1333”
Haque 等 - 1998 - Comparison of infrared, Raman, photoluminescence, DOI: 10.1063/1.367201 -
Acetate confidence 1.0
“For PVC, C H stretching mode can be S.Rameshetal./SpectrochimicaActaPartA66(2007)1237-1242 1239 Table2 VibrationalmodesandwavenumbersexhibitedbyPMMA Wavenumbers(cm-1) Descriptionofvibrations References C Hstretching 2927-2986 [30,32] C Ostr”
Ramesh 等 - 2007 - FTIR studies of PVCPMMA blend based polymer elect DOI: 10.1016/j.saa.2006.06.012 -
Ring structure confidence 1.0
“The two bands at 1333cm-1 first were both assigned to the ring stretch, the one coupled with OH and the 1483 and 1373cm-1 other one with in-plane bending mode (Edwards et al., 2003).”
Lorenz 等 - 2022 - Survival of Xanthoria parietina in simulated space DOI: 10.1017/S1473550422000076 -
Alkyl C-H confidence 1.0
“In addition, the 800 cm-1 bands were allo1333 CH vibrations Monosaccharide galactose, glucos 2”
Maher 等 - 2021 - Optimization of Ultrasound-Assisted Extraction of DOI: 10.3390/antiox10101612 -
Hydroxyl (O-H) confidence 1.0
“stretching and at 1333 and 1453 cm-1 from OH bending of a primary alcohol [27-30].”
Synthesis and Characterization of Inulin-Based Responsive Polyurethanes for Breast Cancer Applications DOI: 10.3390/polym12040865 -
N eq o confidence 1.0
“The band observed at 1332.96 cm-1 circular in shape with smooth edges except some which (curve-1) represent N=O stretching of nitro were irregular in shape (Fig.”
Anthelmintic activity of silver-extract nanoparticles synthesized from the combination of silver nanoparticles and M. charantia fruit extract DOI: 10.1186/s12906-016-1219-5 -
Alkyl C-H confidence 1.0
“2897 C-H stretching Glycerol 1333 C-H deformation 1239”
Zhuang 等 - 2020 - Observation of Potential Contaminants in Processed DOI: 10.3390/app10124345
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