What absorbs at 1656 cm⁻¹ in an FTIR spectrum?
A band near 1656 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 1656 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 | 47 | 41 | 1.0 |
| Carbonyl (C=O) | 15 | 11 | 1.0 |
| Carboxyl (COOH) | 11 | 8 | 1.0 |
| Methacrylate | 11 | 8 | 1.0 |
| Acetate | 11 | 8 | 1.0 |
| Ester | 10 | 7 | 1.0 |
| N h | 9 | 9 | 1.0 |
| Protein alpha helix | 9 | 8 | 1.0 |
| Ketone | 9 | 6 | 1.0 |
| Alkyl C-H | 6 | 6 | 1.0 |
| Hydroxyl (O-H) | 5 | 5 | 1.0 |
| Protein | 5 | 4 | 1.0 |
| Aromatic ring | 4 | 4 | 1.0 |
| Secondary amine | 4 | 4 | 1.0 |
| Alkene (C=C) | 3 | 3 | 1.0 |
| Water (H2O) | 3 | 3 | 1.0 |
| Methoxy (OCH3) | 3 | 2 | 1.0 |
| C n single bond | 2 | 2 | 1.0 |
| Ring structure | 2 | 2 | 1.0 |
| N-O bond | 2 | 2 | 1.0 |
| Protein beta turn | 2 | 1 | 1.0 |
| C-O single bond | 2 | 1 | 1.0 |
| Protein beta sheet | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Amine primary | 1 | 1 | 1.0 |
| Silicate | 1 | 1 | 1.0 |
| Phosphorus | 1 | 1 | 1.0 |
| Phosphate (PO4) | 1 | 1 | 1.0 |
| Methyl | 1 | 1 | 1.0 |
| Nitrate | 1 | 1 | 1.0 |
| Protein random coil | 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 |
|---|---|---|---|
| polyurethane | 1656, 2270, 1700 | 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 1656 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
“A comparison of experimental (in vesicles with 1,2mode responsible for 100% of the intensity of the 1656 band in dipalmitoylphosphatidylcholine) and simulated spectra of the amide I”
Brauner 等 - 2000 - C-13 isotope labeling of hydrophobic peptides. Ori DOI: 10.1021/ja992522o -
Hydroxyl (O-H) confidence 1.0
“The OH stretching band at water.[24] Furthermore, the peaks at change of adsorbed 1656cm(cid:3)1”
Hassan - 2019 - Fourier transform infrared spectroscopy to detect DOI: 10.1080/00387010.2019.1623262 -
Amide confidence 1.0
“For transflection measurements, a peak height at u t cm-1 h 1656 (amide I vibrational mode) was used to segment pixels with an absorbance o greater than 0.015 to ensure that only cells were being counted in the measurement.”
Holton 等 - 2011 - Subcellular localization of early biochemical tran DOI: 10.1039/c1an15112f. -
Protein random coil confidence 1.0
“On the contrary, compared with absorption silka Random coil of 1656 1535 peak of BDO-extended PU, that of Dow BPU decreases in the silka”
Silkinspired polyurethane containing GlyAlaGlyAla tetrapeptide. II. physical properties and structure DOI: 10.1002/app.39185 -
Alkyl C-H confidence 1.0
“cm-1 cm-1, 1656 are vibrating peaks of cis (C=C) and cis (C-H) AND and CDB have spectral similarities at 723”
Martins 等 - 2019 - Approach by Raman and infrared spectroscopy in thr DOI: 10.31349/RevMexFis.65.328 -
N-O bond confidence 1.0
“Middle Eastern collection-PCA of PVAc IR spectra ~1740 As with the PVAc samples, the peak at cm-1 ~1656 PCA was calculated for all 121 PVAc based IR specis most likely due to the NO symmetric”
Identification of cellulose nitrate based adhesive repairs in archaeological pottery of the University of Melbourne’s Middle Eastern archaeological pottery collection using portable FTIR-ATR spectroscopy and PCA DOI: 10.1186/s40494-016-0116-z -
Amide confidence 1.0
“LLM confirmed rule peak-group candidate”
Noguchi 等 - 2001 - Triplet formation on a monomeric chlorophyll in th DOI: 10.1021/bi0019848 -
Amide confidence 1.0
“type of characterization, we will ultimately gain a better proteins are represented by the amide I peak only (1656 understanding of the physiological processes in the seed, as well The highest concentrations of protein were observed in the”
Pietrzak 和 Miller - 2005 - Microchemical structure of soybean seeds revealed DOI: 10.1021/jf050608x
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