What absorbs at 1631 cm⁻¹ in an FTIR spectrum?
A band near 1631 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 1631 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 | 28 | 28 | 1.0 |
| Carbonyl (C=O) | 17 | 17 | 1.0 |
| Methacrylate | 16 | 16 | 1.0 |
| Acetate | 16 | 16 | 1.0 |
| Carboxyl (COOH) | 15 | 14 | 1.0 |
| Ketone | 12 | 12 | 1.0 |
| Ester | 12 | 12 | 1.0 |
| N h | 10 | 9 | 1.0 |
| Hydroxyl (O-H) | 8 | 8 | 1.0 |
| Water (H2O) | 7 | 6 | 1.0 |
| Secondary amine | 7 | 6 | 1.0 |
| Alkene (C=C) | 6 | 6 | 1.0 |
| Aromatic ring | 6 | 6 | 1.0 |
| Alkyl C-H | 5 | 5 | 1.0 |
| C-O single bond | 5 | 5 | 1.0 |
| C n single bond | 4 | 4 | 1.0 |
| Methoxy (OCH3) | 4 | 4 | 1.0 |
| C=n | 3 | 2 | 1.0 |
| Protein | 2 | 2 | 1.0 |
| Protein beta sheet | 2 | 2 | 0.95 |
| Metal oxygen | 1 | 1 | 1.0 |
| N-O bond | 1 | 1 | 1.0 |
| Amine primary | 1 | 1 | 1.0 |
| Carbon dioxide | 1 | 1 | 1.0 |
| Silanol (Si-OH) | 1 | 1 | 1.0 |
| Protein random coil | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 0.9 |
| Chitosan | 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 |
|---|---|---|---|
| silver nanoparticles | 1631, 1636, 1637 | Methacrylate, Acetate, Amide | 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 1631 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
-
Acetate confidence 1.0
“The peaks at 1631 are due to C=O stretching in amide group while the cm-1”
Development of a water dispersible granule (WDG) formulation of Bacillus thuringiensis for the manag DOI: 10.1080/09583157.2021.1895073 -
Hydrogen bond confidence 1.0
“The rate constant (k, of the 4-NP frameworkwaskeptunchangedafterloadingPt1CexonZSM-5.The reduction was taken as the slope of the correlation ln(c0/c) cm(cid:3)1 band at 1631 was due to hydrogen bonding stretching viagainst t (min).”
CO oxidation and 4-nitrophenol reduction over ceria-promoted platinum nanoparticles impregnated with ZSM-5 zeolite DOI: 10.1016/j.jre.2021.07.009 -
confidence 1.0
“A similar FTIR band at 1631 is ascribed to al.46 phase, explaining the blueshift of the chief band according to VegPbI 2-MAI-DMF complex by Guo In fact, the existence of et”
Hydration of mixed halide perovskites investigated by Fourier transform infrared spectroscopy DOI: 10.1063/1.5087914 -
Water (H2O) confidence 1.0
“A moderate cm-1 peak at 1629~1608 was assigned to a δ(N-H) vibration of the glycosidic ligand in the IR cm-1 spectrum of aminated glucose compared to the sharp bands at 1631 attributed to a δ(HOH) cm-1 vibration of crystal water in that of”
Liao 等 - 2011 - Synthesis and Characterization of an Aminated D-gl DOI: 10.4028/www.scientific.net/AMR.197-198.65 -
Hydroxyl (O-H) confidence 1.0
“LLM confirmed rule peak-group candidate”
Mu 等 - 2009 - Synthesis, characterization and photoluminescence DOI: 10.1088/0957-4484/20/34/345602 -
C=n confidence 1.0
“of aromatic aldehydes and CO is indicated by the band at 2856 A protein-specific 2 cm-1 peak at 1631 was linked to the stretching vibrations of the C=N and C=C bonds.”
Biosynthesis and Characterization of Silver Nanoparticles Using Tribulus terrestris Seeds: Revealed Promising Antidiabetic Potentials DOI: 10.3390/molecules28104203 -
Hydroxyl (O-H) confidence 1.0
“Analysis using FTIR in accordance with the characteristics of GO-Fe 4 cm-1 cm-1 cm-1 (O-H stretching), 1631 (C = C aromatic), and 565 (Fe-O).”
Rukman 等 - 2019 - GO-Fe3O4 Nanocomposite from coconut shell Synthes DOI: 10.1088/1755-1315/217/1/012008 -
Aromatic ring confidence 1.0
“Peaks observed at 1631 and 1730 possibly refer to C=C 11 stretching of aromatic rings, N-H vibration of amines and C=O stretching of amides 12 and carboxylic groups [39].”
Cytotoxicity and antibacterial activities of plant-mediated synthesized zinc oxide (ZnO) nanoparticles using Punica granatum (pomegranate) fruit peels extract DOI: 10.1016/j.molstruc.2019.04.026
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