What absorbs at 1635 cm⁻¹ in an FTIR spectrum?
A band near 1635 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 1635 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 |
|---|---|---|---|
| Amide | 41 | 40 | 1.0 |
| Hydroxyl (O-H) | 38 | 36 | 1.0 |
| Water (H2O) | 32 | 30 | 1.0 |
| Alkene (C=C) | 24 | 23 | 1.0 |
| Carbonyl (C=O) | 23 | 22 | 1.0 |
| Carboxyl (COOH) | 21 | 21 | 1.0 |
| Methacrylate | 20 | 20 | 1.0 |
| Acetate | 20 | 20 | 1.0 |
| Ketone | 16 | 16 | 1.0 |
| Ester | 15 | 15 | 1.0 |
| Protein beta sheet | 10 | 10 | 1.0 |
| Alkyl C-H | 9 | 9 | 1.0 |
| Aromatic ring | 7 | 7 | 1.0 |
| N h | 7 | 7 | 1.0 |
| Methoxy (OCH3) | 6 | 6 | 1.0 |
| Protein | 5 | 5 | 1.0 |
| C-O single bond | 5 | 5 | 1.0 |
| Secondary amine | 4 | 4 | 1.0 |
| C n single bond | 3 | 3 | 1.0 |
| Silicon (Si) | 3 | 3 | 1.0 |
| Silanol (Si-OH) | 3 | 3 | 1.0 |
| Carbohydrate | 2 | 2 | 1.0 |
| C c single bond | 2 | 2 | 1.0 |
| Hydrogen bond | 2 | 2 | 1.0 |
| Urea | 2 | 2 | 1.0 |
| Sulfur | 1 | 1 | 1.0 |
| Lipid | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| N-O bond | 1 | 1 | 1.0 |
| Phosphate (PO4) | 1 | 1 | 1.0 |
| Nitrogen heterocycle | 1 | 1 | 1.0 |
| Lewis acid site | 1 | 1 | 1.0 |
| Ammonium | 1 | 1 | 1.0 |
| Methyl | 1 | 1 | 1.0 |
| Urethane | 1 | 1 | 1.0 |
| Fatty acid | 1 | 1 | 1.0 |
| Amino acid | 1 | 1 | 1.0 |
| Oxygen heterocycle | 1 | 1 | 1.0 |
| Nucleic acid | 1 | 1 | 1.0 |
| C=n | 1 | 1 | 0.9 |
| Chitosan | 1 | 1 | 0.8 |
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 |
|---|---|---|---|
| TiO2 | 1635, 1700, 1093 | Hydroxyl (O-H) | 1 |
| TiO2 nanoparticles | 1635, 1700, 455 | Hydroxyl (O-H) | 1 |
| silver nanoparticles | 1635, 1636, 1631 | Hydroxyl (O-H), Amide | 1 |
| apatite | 1635, 3053, 1640 | Amide, Hydroxyl (O-H), 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 1635 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
“LLM confirmed rule peak-group candidate”
Bio-engineered TiO2 nanoparticles using Ledebouria revoluta extract: Larvicidal, histopathological, antibacterial and anticancer activity DOI: 10.1080/03067319.2020.1718668 -
Hydroxyl (O-H) confidence 1.0
“LLM confirmed rule peak-group candidate”
Badri 等 - 2021 - Adsorptive capacity of malachite green onto MgM3+ DOI: 10.30955/gnj.003443 -
confidence 1.0
“Explicit assignment: '1590, 1607, 1635 (vibrational mode of furan)'”
Preparation and evaluation of nanocomposites of polyfuran with Al2O3 and montmorillonite clay DOI: 10.1002/pi.1562 -
Nucleic acid confidence 1.0
“0.1 100 1000 10000 1 10 CS-SP nanoparticle with plasmid DNA, peaks at 3249.04 and 1635.09cm-1 (d, Size nm) shifted from lower frequency wavenumbers to 1635.58cm-1”
Bande 等 - 2015 - Synthesis and Characterization of Chitosan-Saponin DOI: 10.1155/2015/371529 -
confidence 1.0
“Amide I band is important in biological band spectra, it arises from coupled C = O stretching and N-H bending of proteins (1635 cm-1) and is”
Chaber 等 - 2017 - Fourier Transform Infrared (FTIR) spectroscopy of DOI: 10.1016/j.infrared.2017.07.017 -
Amide confidence 1.0
“ObA 50-year-old high myopic male patient had retinal deviously, the maxima amide I and II bands at 1635 and tachment in both eyes and had undergone multiple reticm-1 1554 nal reattachment operations in the past 13 years.”
Chen 等 - 2006 - Corneal calcification chemical composition of cal DOI: 10.1007/s00417-005-1191-0 -
Urea confidence 1.0
“The prominent bonded cm-1 band centred at 1635 corresponds to the hydrogen-bonded ordered urea carbonyl [27].”
Hydrogen bonding and thermomechanical properties of model polydimethylsiloxane based poly(urethane-urea) copolymers: Effect of hard segment content DOI: 10.1016/j.porgcoat.2015.06.015 -
Amide confidence 1.0
“revealed bands at 1634.92, 2156.94, and 3269.31 cm-1 A band at 1634.92 corresponded to the bending vibrations of the amide I and amide II bands of proteins (Gole et al.”
Biosynthesis and characterization of silver nanoparticles using Trichoderma longibrachiatum and their effect on phytopathogenic fungi DOI: 10.1186/s41938-018-0028-1
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