What absorbs at 1331 cm⁻¹ in an FTIR spectrum?
A band near 1331 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 1331 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 |
|---|---|---|---|
| Ring structure | 2 | 2 | 1.0 |
| Alkyl C-H | 2 | 2 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Lignin | 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 |
| Water (H2O) | 1 | 1 | 1.0 |
| Boron nitrogen | 1 | 1 | 1.0 |
| S eq o | 1 | 1 | 0.9 |
| Phosphate (PO4) | 1 | 1 | 0.9 |
Ranking reflects accumulated literature evidence, not a single fixed rule. Always confirm against your sample context.
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 1331 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
-
Boron nitrogen confidence 1.0
“of 745 and when the h-BN addition h-BN additive located at Furthercontent reaches 0.8wt% is interesting, which results more, the Raman peaks shift down to 1331.74 and 𝑠𝑝2 1331.16cm-1 from hybridization B-N-B and B-N vibration, rewhen the ad”
B–C Bond in Diamond Single Crystal Synthesized with h-BN Additive at High Pressure and High Temperature DOI: 10.1088/0256-307X/33/2/028101 -
Alkyl C-H confidence 1.0
“It is understood that morphology is dependent cm(cid:1)1) -CH bending mode vibration (at 1331 indicates that largely on the synthesis method, choice of ingredients and 3”
Nasreen 等 - 2019 - Hybrid mesoporous silicates A distinct aspect to DOI: 10.1016/j.sjbs.2015.08.014 -
Water (H2O) confidence 1.0
“11 of 19 These were also located in spectrum of ionic liquid [C8mim][NTf2] at 1347 cm-1 and 1330 cm-1, while the binding of one of the oxygen atoms of the sulfonic groups of the anion with a water molecule in complex (I) lead to a significa”
Study of Lithium-Extraction Systems Based on Benzo-15-Crown-5 Ether and Alkylimidazolium-BasedIonic Liquid DOI: 10.3390/molecules28030935 -
Ring structure confidence 1.0
“91% Overall SR 82% cm-1 averages of the spectra that were reconstructed from the rethat is likely assigned possibly causing the band at 1331 maining four components show no characteristic paraffin sigto a ring deformation vibration [18, 49,”
Discrimination of grass pollen of different species by FTIR spectroscopy of individual pollen grains DOI: 10.1007/s00216-020-02628-2 -
Alkyl C-H confidence 1.0
“LLM confirmed rule peak-group candidate”
Gu 等 - 2022 - Chemical Component Characterization and Potential DOI: 10.15376/biores.17.2.2525-2546 -
Acetate confidence 1.0
“O-H (3800containing surface groups, namely the stretching (1385 modes, as well as the peak at 1331 attributed cm(cid:3)1 cm(cid:3)1) C-O 09 2800 to the one-phonon diamond mode which was found to appear and 3695 and single bond vibrations li”
Hydroxylation and self-assembly of colloidal hydrogenated nanodiamonds by aqueous oxygen radicals from atmospheric pressure plasma jet DOI: 10.1039/c8ra07873d -
Lignin confidence 1.0
“The FTIR spectra of birch and abies ethanol lignin sulfates [16] obtained in a similar The FTIR spectra of birch and abies ethanol lignin sulfates [16] obtained in a similar way are almost identical, except for the presence in the spectrum”
An Efficient Method of Birch Ethanol Lignin Sulfation with a Sulfaic Acid-Urea Mixture DOI: 10.3390/molecules27196356 -
Hydroxyl (O-H) confidence 1.0
“LLM confirmed rule peak-group candidate”
Liu 等 - 2018 - Highly Efficient Flame Retardant Hybrid Composites DOI: 10.3390/polym10060625
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