What absorbs at 3630 cm⁻¹ in an FTIR spectrum?
A band near 3630 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 3630 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) | 18 | 16 | 1.0 |
| Water (H2O) | 6 | 5 | 1.0 |
| Alkyl C-H | 3 | 2 | 1.0 |
| N h | 2 | 2 | 1.0 |
| Metal hydroxyl | 2 | 2 | 1.0 |
| Methoxy (OCH3) | 1 | 1 | 1.0 |
| Methacrylate | 1 | 1 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| Acetate | 1 | 1 | 1.0 |
| Carboxyl (COOH) | 1 | 1 | 1.0 |
| Bronsted acid site | 1 | 1 | 1.0 |
| Bromine | 1 | 1 | 1.0 |
| Silicon (Si) | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| Silicon-oxygen (Si-O) | 1 | 1 | 0.7 |
| Carbon dioxide | 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 |
|---|---|---|---|
| bentonite | 3630, 882, 918 | Hydroxyl (O-H), Water (H2O) | 3 |
| montmorillonite | 3630, 1637, 523 | Hydroxyl (O-H), Water (H2O) | 2 |
| starch | 3630, 1650, 1540 | Hydroxyl (O-H), Alkyl C-H | 1 |
| nanocomposites | 3630, 1717, 1630 | 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 3630 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
“On the other hand, 3 2 cm-1 exhibits a band at 3630 that belongs to -OH stretching.”
Caliman 等 - 2023 - Gellan Gum-Montmorillonite Nanocomposites for Elec DOI: 10.3390/coatings13020350 -
Metal hydroxyl confidence 1.0
“LLM confirmed rule peak-group candidate”
Mutrofin 等 - 2018 - Physical-chemistry of Nawangan's phyropyllite and DOI: 10.1088/1757-899X/285/1/012026 -
Hydroxyl (O-H) confidence 1.0
“The O-H stretchingspectrumbetween3510cm-1 and3630cm-1”
The Raman jet spectrum of trans-formic acid and its deuterated isotopologs: Combining theory and experiment to extend the vibrational database DOI: 10.1063/5.0039237 -
Hydroxyl (O-H) confidence 1.0
“Absorption bands at 3629.67 and 3741.69 were due to O-H stretch in free hydroxyl groups of starch molecule.”
Singh 和 Sharanagat - 2020 - Physico-functional and structural characterization DOI: 10.1016/j.ijbiomac.2020.07.185 -
Hydroxyl (O-H) confidence 1.0
“LLM confirmed rule peak-group candidate”
Ashiq 等 - 2019 - Municipal solid waste biochar-bentonite composite DOI: 10.1016/j.jenvman.2019.02.006 -
Hydroxyl (O-H) confidence 1.0
“cm-1 In the OH stretching region the band at 3630 stems from vibrations of OH groups cm-1 coordinated to different octahedral cations, the broad band around 3430 is due to stretching vibrations of OH-groups in hydrogen bonded water molecule”
Rehydration Driven Na-Activation of Bentonite—Evolution of the Clay Structure and Composition DOI: 10.3390/ma14247622 -
Alkyl C-H confidence 1.0
“H 2O and C-H Absorption Line However, the antisymmetric stretching vibration absorption of H 2O around 3630 cm-1 was In these samples, the vast majority of samples showed the absorption of H 2O at about not detected in these samples.”
Cai 等 - 2021 - Microdiamonds in Alkalic Dolerites from the North DOI: 10.3390/cryst11111325 -
Hydroxyl (O-H) confidence 1.0
“The cm-1 wide peaks at 3630 and 3420 were hydroxyl stretch vibrations of water intercalated in layers cm-1 of Bent.”
Surface Modification of Bentonite with Polymer Brushes and Its Application as an Efficient Adsorbent for the Removal of Hazardous Dye Orange I DOI: 10.3390/nano10061112
Have a spectrum with this band?
Upload your FTIR spectrum and get a full interpretation report — peak assignments with literature citations, library matches, and a literature-backed analysis — in seconds.