What absorbs at 3421 cm⁻¹ in an FTIR spectrum?
A band near 3421 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 3421 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) | 27 | 27 | 1.0 |
| N h | 8 | 6 | 1.0 |
| Water (H2O) | 5 | 5 | 1.0 |
| Alkyl C-H | 3 | 3 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| Amine primary | 1 | 1 | 0.9 |
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 |
|---|---|---|---|
| polyethylene | 3421, 1737, 1720 | Alkyl C-H, Hydroxyl (O-H) | 1 |
| nanotube | 3421, 1540, 1080 | N h, Hydroxyl (O-H), Alkyl C-H | 1 |
| starch | 3421, 1650, 1540 | Hydroxyl (O-H), Alkyl C-H | 1 |
| nanoparticles | 3421, 1732, 1647 | Alkyl C-H, 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 3421 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
“LLM confirmed rule peak-group candidate”
Arizka 等 - 2019 - Synthesis and Physical Properties Characterization DOI: 10.1088/1757-899X/546/4/042004 -
Hydroxyl (O-H) confidence 1.0
“LLM confirmed rule peak-group candidate”
Study of equilibrium, kinetic and thermodynamic for removal of Pb(II) in aqueous solution using Sago bark (Metroxylon sago) DOI: 10.1063/1.5064078 -
Hydroxyl (O-H) confidence 1.0
“It is stretching vibration appeared at 3421.4 in crystallite area of the films is in consistence with the mechanACAH typical of the polymeric absorption of hydroxyl groups.”
Structure property relations in polyethylene oxide/starch blended films using WAXS techniques DOI: 10.1002/app.37616 -
Water (H2O) confidence 1.0
“The O-H stretching frequencies, which are caused by adsorbed moisture on the surface of ZnO nanoparticles, correspond to the broad peak cantered at 3421 cm-1.”
Kumar 等 - 2021 - Centella asiatica mediated facile green synthesis DOI: 10.1016/j.inoche.2021.108865 -
Water (H2O) confidence 1.0
“Among them, the broad band at 3421 and 1630 Downloaded come from a small quantity of surface-absorbed water, corresponding to the O-H stretching”
Lai 等 - 2013 - Controlled Synthesis of CaWO4 Microcrystalline via DOI: 10.1080/10584587.2013.780145 -
Hydroxyl (O-H) confidence 1.0
“The bands at 3421.4 and La(OH) nanorods taken in the SEM mode is shown in be attributed to the O-H vibration in absorbed water on the of the 3”
Mu 等 - 2009 - Synthesis, characterization and photoluminescence DOI: 10.1088/0957-4484/20/34/345602 -
Hydroxyl (O-H) confidence 1.0
“assigned to O-H stretching”
Rukman 等 - 2019 - GO-Fe3O4 Nanocomposite from coconut shell Synthes DOI: 10.1088/1755-1315/217/1/012008 -
Hydroxyl (O-H) confidence 1.0
“LLM confirmed rule peak-group candidate”
Rout 等 - 2017 - A green approach to produce silver nano particles DOI: 10.1016/j.surfin.2017.03.004
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