What absorbs at 3700 cm⁻¹ in an FTIR spectrum?
A band near 3700 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 3700 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) | 42 | 36 | 1.0 |
| N h | 4 | 4 | 1.0 |
| Amine primary | 3 | 3 | 1.0 |
| Silanol (Si-OH) | 3 | 3 | 1.0 |
| Water (H2O) | 3 | 3 | 1.0 |
| Amide | 2 | 2 | 1.0 |
| Silicon-oxygen (Si-O) | 1 | 1 | 1.0 |
| Aldehyde (CHO) | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| Silicon (Si) | 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 |
|---|---|---|---|
| Cellulose | 3700, 1735, 1650 | Hydroxyl (O-H) | 1 |
| water | 3700, 1018, 2945 | 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 3700 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
“OH-stretching contribution in the region between ~3700 cm-1 and ~3000 cm-1.”
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
“Therefore, the most important deconvolution is presented in this section, as the region 37003000 cm-1 is assigned to the hydroxyl groups present in the biopolymer structure [32,38].”
IR Study on Cellulose with the Varied Moisture Contents: Insight into the Supramolecular Structure DOI: 10.3390/ma13204573 -
Hydroxyl (O-H) confidence 1.0
“LLM confirmed rule peak-group candidate”
Mesoporous magnetite nanoparticles synthesis using the Peltophorum pterocarpum pod extract, their antibacterial efficacy against pathogens and ability to remove a pollutant dye DOI: 10.1016/j.molstruc.2018.10.042 -
Silanol (Si-OH) confidence 1.0
“Absent 5300 Water, combination band v1 Si-OH 3730 stretching (kaolinite, clay) n/a Shoulder Absent Si-OH 3700 stretching, tilted (kaolinite, clay)”
FTIR photoacoustic spectroscopy for identification and assessment of soil components_ Chernozems and their size fractions DOI: 10.1016/j.pacs.2020.100162 -
Hydroxyl (O-H) confidence 1.0
“spectral bands: At above 3700 for free OH and bands cm(cid:2)1 cm(cid:2)1 Thus, it is wholly taken into account in the numerical fitin the regions of 3530-3570 and around 3100 for”
Munoz 等 - 2007 - FTIR study of water clusters in water-triethylamin DOI: 10.1016/j.chemphys.2007.03.015 -
Hydroxyl (O-H) confidence 1.0
“cm-1 The vibrations at 3700 are observed after calcinations which decreasing of O-H bending intensity at 1600 can be assigned for O-H stretching from isolated -OH groups [8].”
Rosyadi 和 Murwani - 2017 - Synthesis and Characterization of Cu Doped Magnesi DOI: 10.1063/1.4978097 -
Silicon (Si) confidence 1.0
“The IR bands intensified cm-1revealed catalyst centered to 273 K and above in the presence of molecular hydroat 1650 and 1635 the presence of hydrogen cm-1, the absorbance band at 3700 which may be attributed interaction with Si(OH)IrO 2and”
IR study of iridium bonded to perturbed silanol groups of Pt-HZSM5 for n-pentane isomerization DOI: 10.1016/j.apcata.2011.12.039 -
Hydroxyl (O-H) confidence 1.0
“a gas-phase CO at 2187 and hydroxyl band at 3700 cm3(cid:3)min(cid:2)1 cm(cid:2)1;”
Tang 和 Chuang - 2014 - In Situ Pulse Diffuse Reflection Infrared Fourier DOI: 10.1366/13-07042
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