What absorbs at 3525 cm⁻¹ in an FTIR spectrum?
A band near 3525 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 3525 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) | 13 | 12 | 1.0 |
| N h | 5 | 4 | 1.0 |
| Water (H2O) | 3 | 3 | 1.0 |
| Secondary amine | 2 | 2 | 1.0 |
| Amide | 1 | 1 | 1.0 |
| N-O bond | 1 | 1 | 1.0 |
| Carboxyl (COOH) | 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 |
|---|---|---|---|
| hematite | 3525, 1030, 469 | Hydroxyl (O-H), Water (H2O) | 1 |
| olivine | 3525, 3564, 3600 | Hydroxyl (O-H), Water (H2O) | 1 |
| collagen | 3525, 1408, 1660 | 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 3525 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
“1618 1625 1625 Asp96 carboxyl 1741 1748 1748 CdO stretching O-H (C) Water Stretching <3525 Wat85 3642 3642”
Maeda 等 - 1999 - Chromophore-protein-water interactions in the L in DOI: 10.1021/bi9907072 -
Hydroxyl (O-H) confidence 1.0
“The wide vibration peak in 3525 9 10 wavelength was related to OH group of water molecules on NPs surface.”
Motaghi 和 Farahmandjou - 2019 - Structural and optoelectronic properties of Ce-Al2 DOI: 10.1088/2053-1591/aaf927 -
Silicon-oxygen (Si-O) confidence 1.0
“also reported that a peak at 3525 is due to "piranha" After the quartz prism was cleaned by solution (3:1 conthe water molecules in the PFSI membrane which the hydrogen bond-”
Humidity dependent structure of water at the interfaces between perfluorosulfonated ionomer thin film and Pt and HOPG studied by sum frequency generation spectroscopy DOI: 10.1016/j.elecom.2012.10.041 -
Hydroxyl (O-H) confidence 1.0
“Finally, when OH peaks 3525±4, and 3480±4 Group II peaks, when”
Peslier 和 Luhr - 2006 - Hydrogen loss from olivines in mantle xenoliths fr DOI: 10.1016/j.epsl.2005.12.019 -
confidence 1.0
“The peaks at 3525, 3397, 1127, 658 and cm-1 600 reflect changes in the aged specimen and are assigned to sulphates detected as their calcium salt (see”
A study of the deterioration of aged parchment marked with laboratory iron gall inks using FTIR-ATR spectroscopy and micro hot table DOI: 10.1186/s40494-016-0083-4 -
Hydroxyl (O-H) confidence 1.0
“The FTIR spectrum of the pure PVPh featured two distinct bands for OH stretching cm-1 vibrations: a sharp band at 3525 corresponding to the free OH units and a very broad band cm-1 centered at 3360 representing self-association hydrogen-bon”
Minimizing the Strong Screening Effect of Polyhedral Oligomeric Silsesquioxane Nanoparticles in Hydrogen-Bonded Random Copolymers DOI: 10.3390/polym10030303 -
Hydroxyl (O-H) confidence 1.0
“The spectra of pure PVPh, phenolic, and BPA feature two distinct bands in the OH-stretching region of cm-1, the FTIR spectra: a very broad band centered at 3350, 3360, and 3330 respectively, representing cm-1, the wide distribution of the h”
Strong Screening Effect of Polyhedral Oligomeric Silsesquioxanes (POSS) Nanoparticles on Hydrogen Bonded Polymer Blends DOI: 10.3390/polym6030926 -
Hydroxyl (O-H) confidence 1.0
“The presence of gypsum (hydrated calcium sulfate-CaSO4·2H2O) is confirmed in samples PK40220 and PK40280 (Figure 3b) via the group of bands visible in the upper region of the spectra (3525, 3400 and 3240 cm-1) and the bands at 1690 and 1620”
Assessment of Easily Accessible Spectroscopic Techniques Coupled with Multivariate Analysis for the Qualitative Characterization and Differentiation of Earth Pigments of Various Provenance DOI: 10.3390/min12060755
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