What absorbs at 931 cm⁻¹ in an FTIR spectrum?
A band near 931 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 931 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 |
|---|---|---|---|
| Methoxy (OCH3) | 4 | 4 | 1.0 |
| Methacrylate | 4 | 4 | 1.0 |
| C-O single bond | 4 | 4 | 1.0 |
| Acetate | 4 | 4 | 1.0 |
| Phosphate (PO4) | 2 | 2 | 1.0 |
| N h | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Amide | 1 | 1 | 1.0 |
| Ammonium | 1 | 1 | 1.0 |
| Carbonate | 1 | 1 | 0.9 |
Ranking reflects accumulated literature evidence, not a single authoritative rule. Always confirm against your sample context.
Possible materials
| Material | Supporting peaks | Overlapping groups | Cited sources |
|---|---|---|---|
| sodium alginate | 931, 1636, 1080 | Methacrylate, C-O single bond, Acetate | 1 |
| curcumin | 931, 1063, 1153 | Methacrylate, Acetate, 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 931 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
-
Phosphate (PO4) confidence 1.0
“Same as 902 cm-1”
Effects of titanium nanoparticles on self-cleaning and structural features of zinc-magnesium-phosphate glass DOI: 10.1016/j.materresbull.2015.11.022 -
Phosphate (PO4) confidence 1.0
“LLM confirmed rule peak-group candidate”
Ascolani Yael 等 - 2014 - Abiotic Degradation of Glyphosate into Aminomethyl DOI: 10.1021/jf502979d -
Ammonium confidence 1.0
“of neat APP is associated with the appearance of the two intense peaks of ammonia at 966 and 931 decomposition of neat APP is associated with the appearance of the two intense peaks of ammonia In Figure 7, the intensities of these typical w”
Development of Bioepoxy Resin Microencapsulated Ammonium-Polyphosphate for Flame Retardancy of Polylactic Acid DOI: 10.3390/molecules24224123 -
Acetate confidence 1.0
“cm-1 agar-specific The band at 931 corresponds to the C-O-O group present in the 3,6 -anhydrogalactose, and cm-1 the bands between 820 and 860 indicate the presence groups[53-57].”
Lima de Castro 等 - 2018 - Polysaccharides of red alga Gracilaria intermedia DOI: 10.1590/0104-1428.013116 -
Acetate confidence 1.0
“3 ScientiFic REpoRTs | 7: | DOI:10.1038/s41598-017-13725-1 13254 www.nature.com/scientificreports/ (cm-1) Frequency Assignment Symmetric C-O stretching from ~931 carbohydrates”
Estimation of the age of human bloodstains under the simulated indoor and outdoor crime scene conditions by ATR-FTIR spectroscopy DOI: 10.1038/s41598-017-13725-1 -
Amide confidence 1.0
“DNAandRNAribose stretching DNAandRNAribose-phosphatechain C-N+-Cstretching 931 vibrationofRNA DNAandRNAribose-phosphatechain C-N+-Cstretching 914”
Fourier-Transform Infrared Spectroscopy as a Discriminatory Tool for Myotonic Dystrophy Type 1 Metabolism: A Pilot Study DOI: 10.3390/ijerph18073800 -
Water (H2O) confidence 1.0
“OeH and that are assigned to stretching vibrations of SieOHandAleAleOH,apeakat3371cm(cid:3)1correspondstoHeOeH 1627cm(cid:3)1 stretching vibrations of interlayer water, a peak at corHeOeH responds to bending mode of adsorbed water, peaks at”
Curcumin encapsulated dual cross linked sodium alginate/montmorillonite polymeric composite beads for controlled drug delivery DOI: 10.1016/j.jpha.2020.07.002 -
Acetate confidence 1.0
“and the stretching vibration of the C-O-C appeared at 930.62 cm-1.”
Synthesis of Phosphated K-Carrageenan and Its Application for Flame-Retardant Waterborne Epoxy DOI: 10.3390/polym10111268
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