What absorbs at 3333 cm⁻¹ in an FTIR spectrum?
A band near 3333 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 3333 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) | 12 | 12 | 1.0 |
| N h | 5 | 5 | 1.0 |
| Alkyl C-H | 3 | 3 | 1.0 |
| Amine primary | 3 | 3 | 1.0 |
| Carbohydrate | 2 | 2 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Methacrylate | 1 | 1 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Carboxyl (COOH) | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| Amide | 1 | 1 | 1.0 |
| Acetate | 1 | 1 | 1.0 |
| N-O bond | 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 |
|---|---|---|---|
| Chitosan | 3333, 1650, 1655 | Alkyl C-H, Hydroxyl (O-H), N h | 1 |
| AgNPs | 3333, 1232, 1048 | Alkyl C-H, N h, Hydroxyl (O-H) | 1 |
| polyurethanes | 3333, 1740, 1728 | N h, Alkyl C-H | 1 |
| polyurethane | 3333, 2270, 1700 | Alkyl C-H, N h | 1 |
| cotton fabric | 3333, 900, 862 | Alkyl C-H, Hydroxyl (O-H) | 1 |
| silver nanoparticles | 3333, 1636, 1631 | Hydroxyl (O-H), Alkyl C-H, N 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 3333 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 hydrolytic degradation of PVA nanofibers in the exposure of phosphate buffer solution (PBS) was confirmed by cm21 ATR-FTIR results in which a change at the intensity of the characteristic peak located at 3333 corresponding to hydroxyl g”
Askari 等 - 2016 - Three-layered electrospun PVAPCLPVA nanofibrous DOI: 10.1002/app.43309 -
Hydroxyl (O-H) confidence 1.0
“Broad peak at 328 cm-1 2923 could represent symmetric C-H stretch of a lone C-H group of tertiary carbon 329 cm-1 components (R 3C-H), and another broader and weak peak at 3333 corresponds -OH group 330 [34, 37, 38].”
Balan 等 - 2021 - Esterification of residual palm oil using solid ac DOI: 10.1016/j.jtice.2012.07.001. -
Hydroxyl (O-H) confidence 1.0
“LLM confirmed rule peak-group candidate”
Burhan 等 - 2020 - Preparation of Cyperus diffusus Vahl cellulose-pol DOI: 10.1088/1757-899X/833/1/012063 -
confidence 1.0
“The sharp peak at 3333 can be assigned to N-H stretching of the primary amines and cm-1 the peak at 2928 corresponding to C-H stretching of”
Biogenic silver nanoparticles: efficient and effective antifungal agents DOI: 10.1007/s13204-015-0463-1 -
Carbohydrate confidence 1.0
“The author analyzed the FTIR ter/intramolecular hydrogen bonds and confirmed the cellulose I transition (3290 cm-1 and bands of inter/intramolecular hydrogen bonds and confirmed the cellulose I transition 3333 cm-1) to cellulose II (3440 cm”
Impact of NaOH Concentration on Deweaving of Cotton Fabric in Aqueous Solutions DOI: 10.3390/su13042015 -
Alkyl C-H confidence 1.0
“The crucial peaks of celcm-1, lulose are -OH stretching and C-H stretching at 3333 and 2881 respectively.”
Fabrication and Evaluation of Water Hyacinth Cellulose-Composited Hydrogel Containing Quercetin for Topical Antibacterial Applications DOI: 10.3390/gels8120767 -
confidence 1.0
“The maximum of the N-H stretching those reported for PU/acrylic systems when increasing the cm-1, vibration band shifts slightly to 3333 indicating an content[34].”
Gabriela Echeverria 等 - 2015 - PolyurethanePoly(2-(Diethyl Amino)Ethyl Methacryl DOI: 10.1590/0104-1428.1716 -
Amine primary confidence 1.0
“A significant change in the intensity of peak was observed for -OH group after ammonium nitrogen adsorption, the position of the peak was shifted from 3332.82 cm-1 to 3270.09 cm-1, and the position of -NH2 group peak was shifted from 1654cm”
Chitosan Modified Zeolite Molecular Sieve Particles as a Filter for Ammonium Nitrogen Removal from Water DOI: 10.3390/ijms21072383
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