What absorbs at 1647 cm⁻¹ in an FTIR spectrum?
A band near 1647 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 1647 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 | 35 | 32 | 1.0 |
| Carbonyl (C=O) | 25 | 21 | 1.0 |
| Methacrylate | 15 | 14 | 1.0 |
| Acetate | 15 | 14 | 1.0 |
| Ketone | 14 | 13 | 1.0 |
| Ester | 14 | 13 | 1.0 |
| Carboxyl (COOH) | 14 | 13 | 1.0 |
| Hydroxyl (O-H) | 11 | 11 | 1.0 |
| Alkene (C=C) | 9 | 9 | 1.0 |
| N h | 7 | 7 | 1.0 |
| Alkyl C-H | 7 | 6 | 1.0 |
| Water (H2O) | 6 | 6 | 1.0 |
| Secondary amine | 6 | 6 | 1.0 |
| Protein | 4 | 4 | 1.0 |
| Carbohydrate | 3 | 3 | 1.0 |
| Aromatic ring | 3 | 3 | 1.0 |
| C n single bond | 3 | 3 | 1.0 |
| Protein random coil | 3 | 3 | 1.0 |
| C-O single bond | 2 | 2 | 1.0 |
| Protein alpha helix | 2 | 2 | 1.0 |
| C=n | 2 | 2 | 1.0 |
| Methoxy (OCH3) | 1 | 1 | 1.0 |
| Carbonate | 1 | 1 | 1.0 |
| Isocyanate | 1 | 1 | 1.0 |
| Urea | 1 | 1 | 1.0 |
| Lignin | 1 | 1 | 1.0 |
| Protein beta sheet | 1 | 1 | 1.0 |
| Metal sulfur | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| C c single bond | 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 |
|---|---|---|---|
| TiO2 | 1647, 1700, 1093 | Methacrylate, Acetate | 1 |
| saliva | 1647, 1648, 1664 | Amide, Methacrylate, Acetate | 1 |
| blood | 1647, 2965, 1117 | Amide, Methacrylate, Acetate | 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 1647 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
-
Alkene (C=C) confidence 1.0
“Moreover, cm-1 weak bands were observed at 1647 and 1540 and assigned to alkenes and aromatic”
Divya 等 - 2018 - Biopolymer gelatin-coated zinc oxide nanoparticles DOI: 10.1016/j.jphotobiol.2017.11.008 -
Amide confidence 1.0
“Blood (A) can easily be distin- (O-H stretch), 3284.3 (H-bonded O-H stretch), 1646.9 cm)1 (amide I random coil), and 1558.8 (amines bend).”
Elkins - 2011 - Rapid Presumptive Fingerprinting of Body Fluids DOI: 10.1111/j.1556-4029.2011.01870.x -
Hydroxyl (O-H) confidence 1.0
“The 181 cm-1 band at 1647 is related to the O-H deformation vibration of water.”
Synthesis of lanthanum tungstate interconnecting nanoparticles by high voltage electrospinning DOI: 10.1016/j.apsusc.2015.05.194 -
Alkene (C=C) confidence 1.0
“LLM confirmed rule peak-group candidate”
Lignin peroxidase isoenzyme: a novel approach to biodegrade the toxic synthetic polymer waste DOI: 10.1080/09593330.2017.1422550 -
Acetate confidence 1.0
“The C=O stretching vibration was found at 1647”
Lee 等 - 2015 - ATR-FTIR and Spectrometric Methods for the Assay o DOI: 10.1080/10942912.2014.923911 -
Hydroxyl (O-H) confidence 1.0
“The FTIR spectrum shows a large peak range because of the vibration cm-1, cm-1 of the O-H stretch at 3700-3200 the peak of the C-H stretches around 2900 and the short peak cm-1 of 1647.21 representing the stretch of OH and C-H from the cell”
Martijanti 等 - 2020 - Investigation of characteristics of bamboo fiber f DOI: 10.1088/1757-899X/850/1/012028 -
Hydrogen bond confidence 1.0
“A broad band peaked at 3350 and a interfacial water which is free from a hydrogen bond with bulk cm-1 relatively sharp band at 1647 can be assigned to the OH”
Nakamura 等 - 2003 - In situ FTIR studies of primary intermediates of p DOI: 10.1021/ja029503q -
Metal sulfur confidence 1.0
“A relatively strong and broad FTIR peaks at 1647 and 670 were observed due to the Cd-S bending and stretching vibration in the surfactant mediated films.”
Effect of Triton X-100 surfactant on thiol-amine cosolvents assisted facile synthesized CdS thin films on glass substrate by spin coating method DOI: 10.1007/s42452-020-2423-y
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