What absorbs at 3620 cm⁻¹ in an FTIR spectrum?
A band near 3620 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 3620 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 |
|---|---|---|---|
| Hydroxyl (O-H) | 32 | 26 | 1.0 |
| Water (H2O) | 4 | 4 | 1.0 |
| Silicon (Si) | 3 | 3 | 1.0 |
| Silicon-oxygen (Si-O) | 2 | 2 | 1.0 |
| Carboxyl (COOH) | 2 | 2 | 1.0 |
| N-O bond | 2 | 1 | 1.0 |
| Amide | 2 | 1 | 1.0 |
| Metal hydroxyl | 1 | 1 | 1.0 |
| Silicate | 1 | 1 | 1.0 |
| Carbonate | 1 | 1 | 1.0 |
| Methacrylate | 1 | 1 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| Acetate | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 0 | 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 |
|---|---|---|---|
| kaolinite | 3620, 3696, 693 | Hydroxyl (O-H), Silicon-oxygen (Si-O), Silicon (Si) | 2 |
| polyvinylpyrrolidone | 3620, 1660, 1700 | Hydroxyl (O-H) | 1 |
| polyvinyl alcohol | 3620, 1141, 1640 | 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 3620 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
-
Hydroxyl (O-H) confidence 1.0
“The presence of similar bands at 3624.3, 3620.4, 3627.1, 3624.5, 3626.7 and 3620.7 cm-1 show the [O-H] stretching of the inner hydroxyl group.”
Unique Halloysite Nanotubes–Polyvinyl Alcohol– Polyvinylpyrrolidone Composite Complemented with Physico–Chemical Characterization DOI: 10.3390/polym9060207 -
Hydroxyl (O-H) confidence 1.0
“Instead, a peak at 3620 which is ("3620," "3480," and "3205," respectively) and the other OH peaks”
Nishihara 等 - 2008 - Effect of chemical environment on the hydrogen-rel DOI: 10.2138/am.2008.2653 -
Hydroxyl (O-H) confidence 1.0
“LLM confirmed rule peak-group candidate”
Rukman 等 - 2019 - GO-Fe3O4 Nanocomposite from coconut shell Synthes DOI: 10.1088/1755-1315/217/1/012008 -
Silicon-oxygen (Si-O) confidence 1.0
“8) showed the 1400cm-1 cm-1, - bending band of COOH at overlaps with the band of presence of quartz and kaolinite with sharp bands at 3698 carboxylate-COO-groupsandis,thereforenot,indicative.Howeverthe 3653cm-1,and~3620cm-1.Thelatterbandove”
The nature of interlayering in clays from a podzol (Spodosol) from the Tatra Mountains, Poland DOI: 10.1016/j.geoderma.2010.10.013 -
Hydroxyl (O-H) confidence 1.0
“LLM confirmed rule peak-group candidate”
Souissi 等 - 2022 - Synthesis, Thermal Properties and Electrical Condu DOI: 10.21203/rs.3.rs-1294285/v1 -
Hydroxyl (O-H) confidence 1.0
“The broad peak at 3620 cm-1 total water amount (7.1%) removed from N-bentonite in the in 3434 which belongs to the OH stretching of H-bonded water”
Tabak 等 - 2011 - Structural analysis of naproxen-intercalated bento DOI: 10.1016/j.cej.2011.09.027 -
Hydroxyl (O-H) confidence 1.0
“In the case of PA-Kaol residue it can be noted the absence of 913cm-1 (Al-OH) and in the region between 3700 and bands at TGA thermograms of kaolinite, OP1311 and a blend of Kaolinite/ 3620cm-1 corresponding to kaolinite hydroxyl groups whi”
Interactions between kaolinite and phosphinate-based flame retardant in Polyamide 6 DOI: 10.1016/j.clay.2018.02.021 -
Hydroxyl (O-H) confidence 1.0
“LLM confirmed rule peak-group candidate”
Cayirli 等 - 2023 - The effect of liquid grinding aids on the dry fine DOI: 10.37190/ppmp/165854
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