What absorbs at 1641 cm⁻¹ in an FTIR spectrum?
A band near 1641 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 1641 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 | 23 | 21 | 1.0 |
| Hydroxyl (O-H) | 17 | 17 | 1.0 |
| Carbonyl (C=O) | 9 | 8 | 1.0 |
| Alkyl C-H | 8 | 8 | 1.0 |
| N h | 8 | 6 | 1.0 |
| Water (H2O) | 7 | 7 | 1.0 |
| Carboxyl (COOH) | 7 | 7 | 1.0 |
| Methacrylate | 6 | 6 | 1.0 |
| Acetate | 6 | 6 | 1.0 |
| Alkene (C=C) | 6 | 5 | 1.0 |
| Ketone | 5 | 5 | 1.0 |
| Ester | 5 | 5 | 1.0 |
| Protein | 3 | 3 | 1.0 |
| C-O single bond | 3 | 3 | 1.0 |
| Secondary amine | 3 | 2 | 1.0 |
| Metal hydroxyl | 2 | 2 | 1.0 |
| Methoxy (OCH3) | 2 | 2 | 1.0 |
| Protein beta sheet | 1 | 1 | 1.0 |
| Protein alpha helix | 1 | 1 | 1.0 |
| Chitosan | 1 | 1 | 1.0 |
| Methyl | 1 | 1 | 1.0 |
| Fatty acid | 1 | 1 | 1.0 |
| Metal oxygen | 1 | 1 | 1.0 |
| N n bond | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Amine primary | 1 | 1 | 1.0 |
| Siloxane (Si-O-Si) | 1 | 1 | 1.0 |
| Silicon-oxygen (Si-O) | 1 | 1 | 1.0 |
| Silicon (Si) | 1 | 1 | 1.0 |
| Phenolic | 1 | 1 | 0.8 |
| C=n | 1 | 0 | 1.0 |
| Ring structure | 1 | 0 | 1.0 |
| Ammonium | 1 | 0 | 1.0 |
| Protein random coil | 1 | 0 | 0.6 |
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 |
|---|---|---|---|
| starch | 1641, 1650, 1540 | Hydroxyl (O-H), Alkyl C-H, Amide | 1 |
| SiO | 1641, 800, 1745 | 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 1641 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”
Microwave assisted acetylation of mung bean starch and the catalytic activity of potassium carbonate in freesolvent reaction DOI: 10.1002/star.201200081 -
Amide confidence 1.0
“LLM confirmed rule peak-group candidate”
Dhasmana 等 - 2019 - Silk fibroin protein modified acellular dermal mat DOI: 10.1016/j.msec.2018.12.038 -
Hydroxyl (O-H) confidence 1.0
“The absorption bands N cm-1 cm-1 around 1641 and 1101 are due to bending of H-O-H absorbed at silica surface A and asymmetric stretching of Si-O-Si, respectively [21].”
Structural and optical investigations of Nd3+doped Y2O3-SiO2 nanopowder DOI: 10.1016/j.jallcom.2017.09.269 -
Hydroxyl (O-H) confidence 1.0
“sharper peak at ~ 1641 indicates the high number The introduction of surfactant CTAC of OH groups on the surface [42].”
Enhanced Hydrophobicity of Nanofibrillated Cellulose Through Surface Modification Using Cetyltrimethylammonium Chloride Derived from Palmityl Alcohol DOI: 10.1007/s12649-021-01366-5 -
Amide confidence 1.0
“LLM confirmed rule peak-group candidate”
JOONSUK - 2019 - ATR-FTIR Analysis of Adhesives Jointing Buddhist S DOI: 10.12654/JCS.2019.35.1.02 -
Hydroxyl (O-H) confidence 1.0
“cm(cid:0) 1 Δρ Moreover, considering that the peak at 1641 was assigned as an (related to the electron SAXS intensity corresponds to an increase in O-H (ρc) density difference between the amylopectin crystalline flakes bending vibration of”
Manipulation of the internal structure of starch by propionyl treatment and its diverse influence on digestion and in vitro fermentation characteristics DOI: 10.1016/j.carbpol.2021.118390 -
confidence 1.0
“The peak at 1641.48 is ambiguous and could represent were assigned to the N-H bending and stretching for primary amine group of residual proteins associated with diatom biosilica which could include the "silaffin" class of silica precipitat”
Mazumder 等 - 2014 - Structural and optical characterization of fresh w DOI: 10.1117/12.2039793 -
Amide confidence 1.0
“LLM confirmed rule peak-group candidate”
Qiu 等 - 2020 - Analyses of the Fourier Transform Infrared Spectra DOI: 10.1134/S0030400X2008041X
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