What absorbs at 1659 cm⁻¹ in an FTIR spectrum?
A band near 1659 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 1659 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 | 24 | 21 | 1.0 |
| Carbonyl (C=O) | 12 | 9 | 1.0 |
| Methacrylate | 11 | 9 | 1.0 |
| Carboxyl (COOH) | 11 | 9 | 1.0 |
| Acetate | 11 | 9 | 1.0 |
| Ketone | 9 | 7 | 1.0 |
| Ester | 9 | 7 | 1.0 |
| N h | 5 | 5 | 1.0 |
| Protein beta sheet | 3 | 3 | 1.0 |
| Secondary amine | 3 | 3 | 1.0 |
| Alkene (C=C) | 3 | 3 | 1.0 |
| Water (H2O) | 2 | 2 | 1.0 |
| Methoxy (OCH3) | 2 | 2 | 1.0 |
| C-O single bond | 2 | 2 | 1.0 |
| Protein alpha helix | 2 | 2 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Phosphate (PO4) | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| C=n | 1 | 1 | 1.0 |
| Carbonate | 1 | 1 | 1.0 |
| Protein random coil | 1 | 1 | 1.0 |
| Protein | 1 | 1 | 1.0 |
| Amine primary | 1 | 1 | 1.0 |
| Alkyl C-H | 1 | 0 | 1.0 |
| Nucleic acid | 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 |
|---|---|---|---|
| chitosan | 1659, 1650, 1655 | Amide, Methacrylate | 2 |
| cellulose | 1659, 1735, 1650 | Methacrylate, Amide | 1 |
| hemicellulose | 1659, 1730, 897 | Methacrylate, Amide, Carbonyl (C=O) | 1 |
| GO | 1659, 1720, 1182 | Methacrylate, Amide, Carboxyl (COOH) | 1 |
| rGO | 1659, 2358, 2930 | Methacrylate, Amide | 1 |
| PCL | 1659, 1751, 1724 | Methacrylate, Carbonyl (C=O), 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 1659 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
-
Amide confidence 1.0
“The bands at 1659, 1599 and 1321 attributable 8 June 2011 Accepted ((cid:2) (ı to the peaks of stretching vibrations of amide I O)), II (N-H)), and the peak of stretching and bending (C Available online 15 June 2011 ((cid:2) (ı vibrations o”
Chen 等 - 2011 - Structural features and bioactivities of the chito DOI: 10.1016/j.ijbiomac.2011.06.009 -
Acetate confidence 1.0
“[19,20,22] Thymine C=O stretching 1659 1659 [19,20,22]”
Han 等 - 2018 - Insight into Rapid DNA-Specific Identification of DOI: 10.3390/molecules23112842 -
Amide confidence 1.0
“3 B) is the cm(cid:2)1 peak, which was previously although it could also correspond to amide II vibration absence of the 1659 a-helix proposed to arisefrom one of the two major subpopu- (34,47).”
Alteration of Sugar-Induced Conformational Changes of the Melibiose Permease by Mutating Arg141 in Loop 4-5 DOI: 10.1016/j.bpj.2009.03.025 -
Amide confidence 1.0
“1550 and in amide II band also corresponded to 1659cm-1 (cid:2)-helical at was assigned to structure.”
Lin 等 - 2005 - PHand thermal-dependent conformational transitio DOI: 10.1016/j.peptides.2004.11.005 -
Acetate confidence 1.0
“The 2 cm-1 absorption band at around 1659 corresponds to -C=O stretching of the cm-1 carbonyl group.”
Rupiasih 等 - 2018 - Study on Transport Properties of Chitosan Membrane DOI: 10.5614/j.math.fund.sci.2018.50.2.6 -
Carboxyl (COOH) confidence 1.0
“Explicit assignment: 'COO- absorptions, at 1659 ... which corresponded to of uronic acids'”
Trigui 等 - 2018 - Physicochemical properties of water-soluble polysa DOI: 10.1016/j.ijbiomac.2018.05.202 -
Amide confidence 1.0
“LLM confirmed rule peak-group candidate”
Proteomic profiling of platelet proteins by trypsin immobilized self-assembled monolayers digestion chip and protein identification using electrospray ionization tandem mass spectrometry DOI: 10.1002/jbm.a.30129 -
Acetate confidence 1.0
“At the same time, there were the appearance of new peaks at 1242 cm-1 and 1659 cm-1 corresponding respectively to C-O vibration of acids”
A novel multicopper oxidase (laccase) from cyanobacteria: Purification, characterization with potential in the decolorization of anthraquinonic dye DOI: 10.1371/journal.
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