What absorbs at 3402 cm⁻¹ in an FTIR spectrum?
A band near 3402 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 3402 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) | 9 | 9 | 1.0 |
| N h | 3 | 2 | 1.0 |
| Alkyl C-H | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Amide | 1 | 1 | 0.9 |
| Water (H2O) | 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 |
|---|---|---|---|
| chitosan | 3402, 1650, 1655 | Alkyl C-H, Hydroxyl (O-H), N h | 1 |
| polydopamine | 3402, 1543, 1707 | Alkyl C-H, N h, Hydroxyl (O-H) | 1 |
| nanocellulose | 3402, 1540, 1646 | 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 3402 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
-
Hydrogen bond confidence 1.0
“LLM confirmed rule peak-group candidate”
Xiao 等 - 2020 - Preparation and characterization of broken-rice st DOI: 10.1016/j.ijbiomac.2020.05.182 -
Hydroxyl (O-H) confidence 1.0
“Bands at 1412 and cm-1 cm-1 1639 represented S=O and C=O stretching, respectively, while bands at 2880 cm-1 and 3402 represented O-H stretching, explaining the possible calcium hydroxide cm-1, cm-1, (CaOH 2) formation.”
Assiry 等 - 2023 - Microstructural and Elemental Characterization of DOI: 10.3390/app13074517 -
Hydroxyl (O-H) confidence 1.0
“The long, sharp cm-1 peak at 3402 indicates the presence of the hydroxyl groups (-OH), the peak at cm-1 2940 indicates the characteristic alkyl groups (C-H) of alkanes, and the peaks at 1634 cm-1 and 1063 indicate the C=C and C-O-C bonds, r”
Application of Plant Surfactants as Cleaning Agents in Shampoo Formulations DOI: 10.3390/pr11030879 -
N h confidence 1.0
“The FTIR spectrum of CS exhibited an absorption band at 3402 cm-1, indicating the overlapping of -OH and -NH stretching vibrations.”
Chen 等 - 2022 - Preparation and Characterization of Nano-Selenium DOI: 10.3390/md20030172 -
Hydroxyl (O-H) confidence 1.0
“The broad band at 3402.47 cm-1 corresponds to (the stretching vibration of nanorods, whereas FTIR (black colored) spectrum confirms the functionalization of CeO2 nanorods 2 cm-1 The broad band at 3402.47 corresponds to (the stretching vibra”
Synthesis of Lipase-Immobilized CeO2 Nanorods as Heterogeneous Nano-Biocatalyst for Optimized Biodiesel Production from Eruca sativa Seed Oil DOI: 10.3390/catal10020231 -
Hydroxyl (O-H) confidence 1.0
“CH 2, CH 3425 OH stretching 3402 OH stretching 3 2884”
Application of Vibrational Spectroscopic Techniques in the Study of the Natural Polysaccharides and Their Cross-Linking Process DOI: 10.3390/ijms24032630 -
Hydroxyl (O-H) confidence 1.0
“According to this Figure, the peak at 3402 cm-1 is related to the stretching vibration of hydroxyl groups (O-H).”
Effect of Nanocellulose Types on Microporous Acrylic Acid/Sodium Alginate Super Absorbent Polymers DOI: 10.3390/jfb13040273 -
Hydroxyl (O-H) confidence 1.0
“Explicit assignment in text.”
Decontamination of fenitrothion from aqueous solutions using rGO/MoS2/Fe3O4 magnetic nanosorbent: synthesis, characterization and removal application DOI: 10.1007/s40201-021-00706-w
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