What absorbs at 1655 cm⁻¹ in an FTIR spectrum?
A band near 1655 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 1655 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 | 87 | 82 | 1.0 |
| Carbonyl (C=O) | 35 | 31 | 1.0 |
| Methacrylate | 25 | 25 | 1.0 |
| Acetate | 25 | 25 | 1.0 |
| Carboxyl (COOH) | 25 | 24 | 1.0 |
| Protein alpha helix | 23 | 20 | 1.0 |
| Ketone | 21 | 21 | 1.0 |
| Ester | 20 | 20 | 1.0 |
| Alkyl C-H | 14 | 14 | 1.0 |
| Alkene (C=C) | 10 | 10 | 1.0 |
| Protein | 10 | 10 | 1.0 |
| Methoxy (OCH3) | 7 | 7 | 1.0 |
| C-O single bond | 7 | 7 | 1.0 |
| N h | 6 | 6 | 1.0 |
| Secondary amine | 4 | 4 | 1.0 |
| Chitosan | 4 | 4 | 1.0 |
| Protein beta sheet | 3 | 3 | 1.0 |
| Hydroxyl (O-H) | 3 | 3 | 1.0 |
| Hydrogen bond | 3 | 3 | 1.0 |
| Aromatic ring | 3 | 2 | 1.0 |
| C n single bond | 2 | 2 | 1.0 |
| Water (H2O) | 2 | 2 | 1.0 |
| N-O bond | 2 | 2 | 1.0 |
| Nucleic acid | 2 | 2 | 1.0 |
| Carbohydrate | 2 | 2 | 1.0 |
| Methyl | 1 | 1 | 1.0 |
| Oxygen heterocycle | 1 | 1 | 1.0 |
| Phosphate (PO4) | 1 | 1 | 1.0 |
| Lipid | 1 | 1 | 1.0 |
| Amino acid | 1 | 1 | 1.0 |
| Lignin | 1 | 1 | 1.0 |
| Protein random coil | 1 | 1 | 1.0 |
| Amine primary | 1 | 1 | 1.0 |
| Aldehyde (CHO) | 1 | 1 | 1.0 |
| C=n | 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 |
|---|---|---|---|
| PVP | 1655, 2983, 1648 | Amide, Methacrylate, Acetate | 1 |
| cellulose | 1655, 1735, 1650 | Acetate, Methacrylate, Amide | 1 |
| starch | 1655, 1650, 1540 | Methacrylate, Acetate, Amide | 1 |
| alginate | 1655, 1100, 1715 | 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 1655 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
“Immediately after between absorbance values of the amide-I peak at 1655 μl), sample preparation in reaction tubes (15 to 25 as previously 0.4 and 0.9, were analyzed per each multivariate training model described, sterile saline (0.9% NaCl)”
Baldauf 等 - 2007 - Effect of selective growth media on the differenti DOI: 10.1016/j.mimet.2006.06.012 -
Carbohydrate confidence 1.0
“Apart from the disappearimately 1655 was the bending vibration absorption cm-1 ance of the corresponding diffraction peaks, the starch peak of H 2O, and that at approximately 1546 was an crystallite region becomes smaller and the amorphous”
Cao 等 - 2020 - Optimization of the preparation process of mung be DOI: 10.1515/ijfe-2020-0025 -
Amide confidence 1.0
“LLM confirmed rule peak-group candidate”
The Antibacterial Activities and Characterizations of Biosynthesized Zinc Oxide Nanoparticles, and Their Coated with Alginate Derived from Fucus vesiculosus DOI: 10.3390/polym15102335 -
Carbonyl (C=O) confidence 1.0
“cm-1 band of 1655 1160 and 898 under both species which is attributed to the impact of increase carbonyl stretching band as”
A Microscopic Study of Paper Decayed by Trichoderma harzianum and Paecilomyces variotii DOI: 10.1007/s10924-017-1147-6 -
Amide confidence 1.0
“LLM confirmed rule peak-group candidate”
Gene-Transformation-Induced Changes in Chemical Functional Group Features and Molecular Structure Conformation in Alfalfa Plants Co-Expressing Lc-bHLH and C1-MYB Transcriptive Flavanoid Regulatory Genes: Effects of Single-Gene and Two-Gene Insertion DOI: 10.3390/ijms18030664 -
Amide confidence 1.0
“cm-1, aromatic-CH attributed to in plane band at 1230 cm-1 deformation, with the band at 1706 attributed to cm-1 acid-COOH, | 3.4 Regression coefficients analysis carboxylic with the band at 1655 attributed to amide I and aromatic C C (Bart”
Identifying the fingerprint of permanganate oxidizable carbon as a measure of labile soil organic carbon using Fourier transform mid‐infrared photoacoustic spectroscopy DOI: 10.1111/ejss.13085 -
Amide confidence 1.0
“LLM confirmed rule peak-group candidate”
In Situ Viscoelasticity Behavior of Cellulose–Chitin Composite Hydrogels during Ultrasound Irradiation DOI: 10.3390/gels7030081 -
Acetate confidence 1.0
“2929 C=O stretching 1655 1652 1646 1646 CH wagging”
Investigations of biodegradable polymer blend electrolytes based on Cornstarch: PVP: NH4Cl and its potential application in solid-state batteries DOI: 10.1007/s10854-021-05266-1
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