What absorbs at 3695 cm⁻¹ in an FTIR spectrum?
A band near 3695 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 3695 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) | 16 | 15 | 1.0 |
| Water (H2O) | 3 | 3 | 1.0 |
| Hydrogen bond | 2 | 2 | 1.0 |
| Silicon-oxygen (Si-O) | 2 | 2 | 1.0 |
| Metal hydroxyl | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| Siloxane (Si-O-Si) | 1 | 1 | 1.0 |
| Carbohydrate | 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 |
|---|---|---|---|
| polyvinylpyrrolidone | 3695, 1660, 1700 | Hydroxyl (O-H) | 1 |
| polyvinyl alcohol | 3695, 1141, 1640 | Hydroxyl (O-H) | 1 |
| kaolinite | 3695, 3696, 693 | Hydroxyl (O-H), Silicon-oxygen (Si-O), 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 3695 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
“The spectra of [O-H] stretching of the inner-surface hydroxyl of S01, S02, S03, S04, cm-1, S05, and S06 show similar absorption bands at 3695.3, 3694.8, 3695.2, 3695.4, 3695.5 and 3695.9 cm-1 respectively.”
Unique Halloysite Nanotubes–Polyvinyl Alcohol– Polyvinylpyrrolidone Composite Complemented with Physico–Chemical Characterization DOI: 10.3390/polym9060207 -
Hydroxyl (O-H) confidence 1.0
“cm-1 Briefly, the broad band between 3695 and 3000 has been attributed to the hydroxyl groups due to associated moisture or intra-molecular hydroxyl groups of the glucose cm-1 monomers [41].”
Starch-based xerogels: Effect of acetylation on Physicochemical and rheological properties DOI: 10.1016/j.ijbiomac.2017.01.101 -
Hydroxyl (O-H) confidence 1.0
“The broad band between 3695 and 3000 has been attributed to the hydroxyl due 181 to associated moisture or intramolecular hydroxyl groups of the glucose monomers (Fang, cm-1 182 Fowler, Sayers, & Williams, 2004) while the peak at 2900 has b”
Nep 等 - 2016 - Rheological and structural properties of modified DOI: 10.1016/j.foodhyd.2016.02.037 -
Hydroxyl (O-H) confidence 1.0
“cm-1 Peaks at 3260, 3400, 3620, 3669, and 3695 are all linked to the vibration of -OH groups Peaks at 3260, 3400, 3620, 3669, and 3695 cm-1 are all linked to the vibration of -OH groups different cm-1 belonging to clay minerals.”
Varrica 等 - 2019 - ATR-FTIR Spectral Analysis and Soluble Components DOI: 10.3390/ijerph16142507 -
Hydroxyl (O-H) confidence 1.0
“LLM confirmed rule peak-group candidate”
Weng 等 - 2020 - Black carbon enriches short-range-order ferrihydri DOI: 10.1016/j.scitotenv.2020.138195 -
confidence 1.0
“2A cm-1 cm-1 186 (1), the bond at 661 is originated from the vibration of the Si-O-Si, 3695 cm-1 cm-1 187 and 3620 are the characteristic peaks of HNTs, and 1653 is generated from”
4-Aminothiophenol capped Halloysite Nanotubes/Silver Nanoparticles as Surface-enhanced Raman Scattering Probe for In-situ Derivatization and Selective Determination of Nitrite Ions in Meat Product DOI: 10.1016/j.talanta.2020.121366 -
Hydroxyl (O-H) confidence 1.0
“The intensely strong peak at 3695 corresponds to hydroxyl deformation modes.”
The Physico-Chemical and Mineralogical Characterization of Mg-Rich Synthetic Gypsum Produced in a Rare Earth Refining Plant DOI: 10.3390/su13094840 -
Hydroxyl (O-H) confidence 1.0
“LLM confirmed rule peak-group candidate”
Cankaya 等 - 2021 - Preparation of poly(MPAEMA)halloysite Nanocomposi DOI: 10.29356/jmcs.v65i2.1257
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