What absorbs at 3500 cm⁻¹ in an FTIR spectrum?
A band near 3500 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 3500 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) | 151 | 142 | 1.0 |
| N h | 35 | 31 | 1.0 |
| Water (H2O) | 24 | 22 | 1.0 |
| Alkyl C-H | 16 | 14 | 1.0 |
| Hydrogen bond | 12 | 12 | 1.0 |
| Secondary amine | 10 | 10 | 1.0 |
| Amide | 10 | 9 | 1.0 |
| Carboxyl (COOH) | 9 | 9 | 1.0 |
| Silanol (Si-OH) | 8 | 7 | 1.0 |
| Carbonyl (C=O) | 7 | 7 | 1.0 |
| Methacrylate | 6 | 6 | 1.0 |
| Acetate | 6 | 6 | 1.0 |
| Alkene (C=C) | 4 | 4 | 1.0 |
| C n single bond | 4 | 4 | 1.0 |
| N-O bond | 4 | 4 | 1.0 |
| Ester | 4 | 4 | 1.0 |
| Aromatic ring | 3 | 3 | 1.0 |
| Carbohydrate | 3 | 3 | 1.0 |
| Methoxy (OCH3) | 3 | 3 | 1.0 |
| C-O single bond | 3 | 3 | 1.0 |
| Ketone | 3 | 3 | 1.0 |
| Silicon-oxygen (Si-O) | 3 | 2 | 1.0 |
| Amine primary | 2 | 2 | 1.0 |
| Carbonate | 2 | 2 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Phosphate (PO4) | 1 | 1 | 1.0 |
| Adsorbed carbon monoxide | 1 | 1 | 1.0 |
| Protein | 1 | 1 | 1.0 |
| Metal oxygen | 1 | 1 | 1.0 |
| C=n | 1 | 1 | 1.0 |
| Metal hydroxyl | 1 | 1 | 1.0 |
| Methyl | 1 | 1 | 1.0 |
| Carbon dioxide | 1 | 1 | 1.0 |
| Sulfate (SO4) | 1 | 1 | 1.0 |
| N n bond | 1 | 1 | 1.0 |
| Lignin | 1 | 1 | 1.0 |
| Silicate | 1 | 1 | 1.0 |
| Thiol | 1 | 1 | 0.7 |
| Siloxane (Si-O-Si) | 1 | 0 | 1.0 |
| Nitrate | 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 |
|---|---|---|---|
| PMMA | 3500, 1722, 1383 | Alkyl C-H | 1 |
| saliva | 3500, 1648, 1664 | Alkyl C-H | 1 |
| blood | 3500, 2965, 1117 | Hydroxyl (O-H) | 1 |
| copper | 3500, 1636, 1202 | Water (H2O), Hydroxyl (O-H) | 1 |
| ZnS | 3500, 1650, 1116 | Water (H2O), Hydroxyl (O-H), Alkyl C-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 3500 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
-
confidence 1.0
“NH 2 It is stated that in amines, the N H stretching vibraCoumarins have two characteristically strong absorption 3500-3300cm-1.”
Arjunan 等 - 2007 - Fourier transform infrared and Raman spectral assi DOI: 10.1016/j.saa.2006.09.044 -
Hydroxyl (O-H) confidence 1.0
“39 cm-1 The broad absorption peak around 3500 is the -OH stretching vibration and the strong band at”
Ataei 等 - 2020 - Electrosprayed PMMA microcapsules containing green DOI: 10.1088/1361-665X/ab9754 -
Silicate confidence 1.0
“The silane-modified NaeMt 29Si pattern of NMR spectrum of in DMF cm-1 eOH band after 3500 is associated with metal groups in silicate medium is presented in Fig.”
Silane functionalization of sodium montmorillonite nanoclay_ The effect of dispersing media on intercalation and chemical grafting DOI: 10.1016/j.clay.2017.12.020 -
Hydroxyl (O-H) confidence 1.0
“ICARTT spectra clusters, database standards, and standard absorption spectra for these compounds are laboratory standard spectra showing phenol absorption at 3500 cm-1.”
Bahadur 等 - 2010 - Phenol Groups in Northeastern US Submicrometer Aer DOI: 10.1021/es9032277 -
Hydroxyl (O-H) confidence 1.0
“LLM confirmed rule peak-group candidate”
Investigation of structural, optical and morphological properties of copper doped zinc sulphide nanoparticles DOI: 10.1016/j.mssp.2016.03.019 -
Water (H2O) confidence 1.0
“populations of bound water by deconvolution of the broad water absorption peak around 3500 A linear dependence of the adduct decay rate constant on the concentration of double and triple hydrogen-bonded waters strongly suggests that the add”
Chan 和 Bogomolni - 2012 - Structural Water Cluster As a Possible Proton Acce DOI: 10.1021/jp304934t -
N-O bond confidence 1.0
“Before immersion, a broad band between 3300 shows that there was no detachment or decohesion of cm(cid:2)1 was assigned to fundamental stretching and 3500 the coatings from the substrate.”
Devi 等 - 2011 - Synthesis and characterization of nanoporous sodiu DOI: 10.1007/s11998-011-9344-z -
Hydroxyl (O-H) confidence 1.0
“cm)1) and water and hydroxyls in the O-H stretch (3500the results of experiments with human blood, peppermint lotion, lip1600 cm)1) cm)1 region.”
Elkins - 2011 - Rapid Presumptive Fingerprinting of Body Fluids DOI: 10.1111/j.1556-4029.2011.01870.x
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