What absorbs at 3400 cm⁻¹ in an FTIR spectrum?
A band near 3400 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 3400 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) | 325 | 294 | 1.0 |
| Water (H2O) | 68 | 60 | 1.0 |
| N h | 43 | 41 | 1.0 |
| Alkyl C-H | 31 | 31 | 1.0 |
| Hydrogen bond | 28 | 26 | 1.0 |
| Amide | 15 | 14 | 1.0 |
| Carbohydrate | 11 | 11 | 1.0 |
| Secondary amine | 11 | 11 | 1.0 |
| Carboxyl (COOH) | 11 | 10 | 1.0 |
| C-O single bond | 10 | 10 | 1.0 |
| Acetate | 10 | 10 | 1.0 |
| Methacrylate | 9 | 9 | 1.0 |
| Aromatic ring | 8 | 7 | 1.0 |
| Silanol (Si-OH) | 8 | 7 | 1.0 |
| Methoxy (OCH3) | 6 | 6 | 1.0 |
| Carbonyl (C=O) | 6 | 6 | 1.0 |
| Silicon-oxygen (Si-O) | 6 | 5 | 1.0 |
| Amine primary | 6 | 5 | 1.0 |
| Silicon (Si) | 5 | 5 | 1.0 |
| Metal oxygen | 5 | 4 | 1.0 |
| Ester | 4 | 4 | 1.0 |
| Protein | 3 | 3 | 1.0 |
| Ketone | 3 | 3 | 1.0 |
| Metal hydroxyl | 2 | 2 | 1.0 |
| N-O bond | 2 | 2 | 1.0 |
| Carbonate | 2 | 2 | 1.0 |
| Lignin | 2 | 2 | 1.0 |
| Amino acid | 2 | 2 | 1.0 |
| Alkene (C=C) | 2 | 2 | 1.0 |
| Phenolic | 2 | 2 | 0.95 |
| Bromine | 1 | 1 | 1.0 |
| Ammonium | 1 | 1 | 1.0 |
| S eq o | 1 | 1 | 1.0 |
| Chlorine | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| C=n | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Protein random coil | 1 | 1 | 1.0 |
| Nitrate | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| Carbon dioxide | 1 | 1 | 1.0 |
| Fatty acid | 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 |
|---|---|---|---|
| PET | 3400, 1408, 800 | Alkyl C-H, N h | 1 |
| calcium phosphate | 3400, 1070, 1149 | Hydroxyl (O-H), Alkyl C-H | 1 |
| SnO2 | 3400, 2800, 1547 | Hydroxyl (O-H), Alkyl C-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 3400 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
-
Water (H2O) confidence 1.0
“The cm-1account bands around 3400 and 1630 for the presprominent The modes A 1g, B 1g, B and Eg are Raman active while A and 2g 2u ence of absorbed molecular water.”
Azam 等 - 2012 - Effect of Mn doping on the structural and optical DOI: 10.1016/j.jallcom.2012.01.072 -
Carbonyl (C=O) confidence 1.0
“FTIR ~3400cm-1 cm-1 analysis shows the intensity peak represent carbonyl at and ester at ~1100 decreased.”
Aziz 等 - 2018 - The effect of Pineapple Leaf Fiber (PALF) incorpor DOI: 10.1088/1755-1315/105/1/012082 -
Carbohydrate confidence 1.0
“The FTIR spectral features of the extractive free enset fiber and stalk (Fig 5) show similar cm-1, cm-1, cm-1, cm-1 cm-1 peaks around 3400 2945 1746 1380 and 1033 which correspond to different functional groups of cellulose, hemicelluloses”
Characterization of crop residues from false banana /Ensete ventricosum/ in Ethiopia in view of a full-resource valorization DOI: 10.1371/journal.pone.0199422 -
Hydroxyl (O-H) confidence 1.0
“When analyzing the spectrum of Ce-HAp, it is possible to observe a band at 3400 cm-1 3400 corresponding to the stretching of OH groups from the Ce-doped hydroxyapatite structure,”
Development of Composite Scaffolds Based on Cerium Doped-Hydroxyapatite and Natural Gums—Biological and Mechanical Properties DOI: 10.3390/ma12152389 -
Hydrogen bond confidence 1.0
“The absorption below 3400 cm~1, nol.20,21 The liquid phase spectrum shows a typical broad where larger clusters with cooperative hydrogen bond hydrogen-bonded OH-stretching absorption with no sizeable sequences are expected to absorb, is le”
Borho 等 - 2001 - Chiral self-recognition in the gas phase the case DOI: 10.1039/b102382a -
N h confidence 1.0
“cm-1, Th e broad band at 3400 pronounced in the LF, is due to Soil samples from the 0to 20-cm depth were separated into parOH or NH stretching typical in crop residues (Haberhauer and ticle-size fractions.”
Calderon 等 - 2011 - Chemical Differences in Soil Organic Matter Fracti DOI: 10.2136/sssaj2009.0375 -
Hydroxyl (O-H) confidence 1.0
“The OH-stretching band at 3400 became w/w, more and more intense when the water content reached 80% indicating that at this hydration state, there are two populations of water molecules representing the first and the”
Hydrating Capabilities of the Biopolymers Produced by the Marine Thermophilic Bacillus horneckiae SBP3 as Evaluated by ATR-FTIR Spectroscopy DOI: 10.3390/ma15175988 -
Hydroxyl (O-H) confidence 1.0
“This cation-exchange process which implies the initial hydroxyl-stretching region at 3400(cid:1)3300 2O in the red mud”
Castaldi 等 - 2008 - XRD, FTIR, and thermal analysis of bauxite ore-pro DOI: 10.1346/CCMN.2008.0560407
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