What absorbs at 3420 cm⁻¹ in an FTIR spectrum?
A band near 3420 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 3420 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) | 45 | 44 | 1.0 |
| Water (H2O) | 9 | 9 | 1.0 |
| N h | 9 | 9 | 1.0 |
| Alkyl C-H | 5 | 5 | 1.0 |
| Methacrylate | 3 | 3 | 1.0 |
| Acetate | 3 | 3 | 1.0 |
| Secondary amine | 3 | 3 | 1.0 |
| Amide | 3 | 2 | 1.0 |
| Silanol (Si-OH) | 3 | 2 | 1.0 |
| Methoxy (OCH3) | 2 | 2 | 1.0 |
| C-O single bond | 2 | 2 | 1.0 |
| Hydrogen bond | 2 | 2 | 1.0 |
| Silicon (Si) | 2 | 2 | 1.0 |
| Ester | 2 | 2 | 1.0 |
| Methyl | 1 | 1 | 1.0 |
| Metal hydroxyl | 1 | 1 | 1.0 |
| Amine primary | 1 | 1 | 1.0 |
| S eq o | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Lignin | 1 | 1 | 1.0 |
| Carbon dioxide | 1 | 1 | 1.0 |
| N-O bond | 1 | 1 | 1.0 |
| Alkene (C=C) | 1 | 1 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Carboxyl (COOH) | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| Siloxane (Si-O-Si) | 1 | 1 | 1.0 |
| Silicon-oxygen (Si-O) | 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 |
|---|---|---|---|
| montmorillonite | 3420, 1637, 523 | Hydroxyl (O-H), Water (H2O) | 1 |
| bentonite | 3420, 882, 918 | Hydroxyl (O-H), Water (H2O) | 1 |
| olivine | 3420, 3525, 3564 | Hydroxyl (O-H), Water (H2O) | 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 3420 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
-
N h confidence 1.0
“The position of 3420cm-1 NH stretching vibration appears from 3500 to C O stretching vibration is particularly clear and is sensitive to 2 and the symmetric NH stretching is observed in the range O stretchits environment in the infrared [73”
Arjunan 等 - 2007 - Fourier transform infrared and Raman spectral assi DOI: 10.1016/j.saa.2006.09.044 -
Hydroxyl (O-H) confidence 1.0
“C-H (aliphatic), and O-H are attributed to the bands at 1422, 1608, 2931, and 3420 cm-1 cm-1 cm-1 O-H stretching at 3458 and C-H stretching at 2902 are both absorption bands [26].”
Aziz 等 - 2022 - The Study of Ion Transport Parameters in MC-Based DOI: 10.3390/membranes12020139 -
Hydroxyl (O-H) confidence 1.0
“[33], who reported that the FTIR spectra of ZnO U cm-1, showed a broad band at 3420 which was assigned to the O-H stretching mode of the N hydroxyl group.”
Divya 等 - 2018 - Biopolymer gelatin-coated zinc oxide nanoparticles DOI: 10.1016/j.jphotobiol.2017.11.008 -
Hydroxyl (O-H) confidence 1.0
“-OH stretching, hydration - - 3422 -OH stretching, hydration 3420”
Hayati-Ashtiani - 2012 - Use of FTIR Spectroscopy in the Characterization o DOI: 10.1080/02726351.2011.615895 -
Water (H2O) confidence 1.0
“respectively.16 as plus peaks at 3420 and 1726 stretching vibrations of while those due to SO 3H and 1, The one at (cid:238) (cid:238) 3 Water in Nafion Membranes J.”
Iwamoto 等 - 2002 - Water in perfluorinated, sulfonic acid Nafion memb DOI: 10.1021/jp013709g -
C-O single bond confidence 1.0
“Meanwhile, for the SLN spectrum, cm-1 the absorption peak centered at 3420 corresponds -C-OH stretching vibration, and weak cm-1 represent C=C stretching vibration, -OH absorption peaks at 1639, 1370 and 1090 deformation vibration and -C-O”
Kim 和 Kang - 2012 - Fabrication of large area photonic crystal with su DOI: 10.1117/12.930432 -
Amide confidence 1.0
“1655cm(cid:2)1 II0 HI spectra are similar in the amide A/B and amide In contrast, the bands (3420, peak reaches its maximum level in less”
Nault 等 - 2013 - Human insulin adsorption kinetics, conformational DOI: 10.1016/j.actbio.2012.09.025 -
Water (H2O) confidence 1.0
“Cross sections of these the fluid inclusions (no identical molecular-water olivines reveal bell-shaped profiles with the highest cm-1 band centered at 3420 intensities in the grain centers (Fig.”
Peslier 和 Luhr - 2006 - Hydrogen loss from olivines in mantle xenoliths fr DOI: 10.1016/j.epsl.2005.12.019
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