What absorbs at 1650 cm⁻¹ in an FTIR spectrum?
A band near 1650 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
Possible functional-group assignments
| Functional group | Supporting facts | Cited sources | Top confidence |
|---|---|---|---|
| Amide | 85 | 64 | 1.0 |
| Carbonyl (C=O) | 32 | 28 | 1.0 |
| Water (H2O) | 11 | 8 | 1.0 |
| Protein alpha helix | 10 | 7 | 1.0 |
| N h | 6 | 6 | 1.0 |
| Hydroxyl (O-H) | 6 | 5 | 0.9 |
| Carboxyl (COOH) | 4 | 4 | 0.9 |
| Alkene (C=C) | 3 | 3 | 0.9 |
| Aromatic ring | 3 | 3 | 0.9 |
| Protein | 2 | 2 | 0.9 |
| C-O single bond | 2 | 2 | 0.9 |
| C n single bond | 2 | 2 | 0.8 |
| C=n | 1 | 1 | 0.8 |
| Sulfur heterocycle | 1 | 1 | 0.8 |
| Protein random coil | 1 | 1 | 0.8 |
| Hydrogen bond | 1 | 1 | 0.8 |
| C c single bond | 1 | 1 | 0.8 |
| Carbohydrate | 1 | 1 | 0.7 |
| Lignin | 1 | 1 | 0.7 |
| Ammonium | 1 | 1 | 0.7 |
Ranking reflects accumulated literature evidence, not a single authoritative rule. Always confirm against your sample context.
Literature behind these assignments
-
N h confidence 1.0
“the relatively interference free region in which it occurs, the mode occurs in the Raman at Other vibrations, C the in-plane NH deformation vibration falls from 1650 to O stretching band is reasonably easy to recognise.”
Arjunan 等 - 2007 - Fourier transform infrared and Raman spectral assi DOI: 10.1016/j.saa.2006.09.044 -
Amide confidence 1.0
“CdO cm-1, the band in the ester group at 1751 that of 1700 cm-1 CdO cm-1 On the other hand, the Acesulfame-K band at 945 does due to the stretch in carboxylic acids, and the band CdO cm-1 not overlap with any Aspartame band, but the low sig”
Armenta 等 - 2004 - FTIR determination of aspartame and acesulfame-k i DOI: 10.1021/jf049218l -
Water (H2O) confidence 1.0
“Text: 'H-O-H was ascribed to bending vibration; the band at 1650'”
Liu 等 - 2012 - Modifications of structure and physicochemical pro DOI: 10.1016/j.lwt.2011.10.012 -
Water (H2O) confidence 1.0
“Explicit assignment: 'peak at 1650 indicated the presence of absorbed water'.”
Rosyadi 和 Murwani - 2017 - Synthesis and Characterization of Cu Doped Magnesi DOI: 10.1063/1.4978097 -
Amide confidence 1.0
“Text: 'this peak shifts to 1650 representative of an alpha-helical protein structure'”
Gough 等 - 2020 - Air-Jet Spun Corn Zein Nanofibers and Thin Films w DOI: 10.3390/ijms21165780 -
Amide confidence 1.0
“Explicit assignment in text: 'two characteristic peaks at 1650 (Amide I) and 1524 (Amide II) cm-1'”
Ivanov 等 - 2021 - AFM and FTIR Investigation of the Effect of Water DOI: 10.3390/molecules26020306 -
Water (H2O) confidence 1.0
“Explicit assignment: 'water 1650cm-1 of the amount of water vapor sorbed in the polymer with the bending vibration'”
Metz 等 - 2005 - Mixed gas water vaporN-2 transport in poly(ethyle DOI: 10.1016/j.memsci.2005.05.010 -
Amide confidence 1.0
“explicit assignment”
Pegado 等 - 2018 - First evidence of microplastic ingestion by fishes DOI: 10.1016/j.marpolbul.2018.06.035
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