What absorbs at 1682 cm⁻¹ in an FTIR spectrum?
A band near 1682 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 1682 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 | 9 | 8 | 1.0 |
| Carbonyl (C=O) | 7 | 6 | 1.0 |
| Methacrylate | 5 | 5 | 1.0 |
| Ketone | 5 | 5 | 1.0 |
| Ester | 5 | 5 | 1.0 |
| Carboxyl (COOH) | 5 | 5 | 1.0 |
| Acetate | 5 | 5 | 1.0 |
| Protein beta sheet | 3 | 3 | 1.0 |
| Alkyl C-H | 2 | 2 | 1.0 |
| Urea | 1 | 1 | 1.0 |
| Lipid | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| Nucleic acid | 1 | 1 | 1.0 |
| Sulfate (SO4) | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Protein | 1 | 1 | 1.0 |
| N-O bond | 1 | 1 | 1.0 |
Ranking reflects accumulated literature evidence, not a single fixed rule. Always confirm against your sample context.
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 1682 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
-
N-O bond confidence 1.0
“Obviously, there were no peaks unique peak at 1682 due to predominate peak of 250(cid:3)C, found”
Thermoanalytical and Fourier transform infrared spectral curve-fitting techniques used to investigate the amorphous indomethacin formation and its physical stability in Indomethacin-Soluplus® solid dispersions DOI: 10.1016/j.ijpharm.2015.10.042 -
Protein confidence 1.0
“cm-1 region A minor peak at 1682 preparations due to different sequences and protein composi-”
Okubo 等 - 2007 - Perturbation of the structure of P680 and the char DOI: 10.1021/bi700157n -
Alkyl C-H confidence 1.0
“with lesser intensity, the same peak is observed in the Raman spectrum, centered at 1682 Three less pronounced bands found for artepillin C in the Raman spectrum were also identified and assigned to C-H stretching, C-H deformation and O-H +”
EXPRESS: Vibrational Spectroscopic Characterization and Coherent Anti-Stokes Raman Spectroscopy (CARS) Imaging of Artepillin C DOI: 10.1177/0003702820904456 -
Protein beta sheet confidence 1.0
“cm-1, the parallel beta sheet band of 1682 the band intensity ∼80% significantly dropped by before 3 h and remained low until 24 h (Fig.”
Shi 等 - 2018 - Biochemical alterations of Candida albicans during DOI: 10.1039/c8an01452c -
Hydroxyl (O-H) confidence 1.0
“The IR spectrum is dominated by the bands ascribed to gypsum at 3484 and 3398 (-OH stretch), cm-1 ν 1682 and 1619 (-OH deformation), 1095 (sulfate stretch), and 667 and 594 (sulfate 3”
New Insights into the Medieval Hispano-Muslim Panel Painting: The Alfarje Found in a Balearic Casal (Spain) DOI: 10.3390/molecules28031235 -
Sulfate (SO4) confidence 1.0
“cm-1 4·2H (CaSO 2O), The frequency peaks at 3535 and 3404 are assigned to gypsum cm-1 and the bands appearing around 1682 and 1620 correspond to sulfate stretching in gypsum [96].”
Systematic Search Using the Proknow-C Method for the Characterization of Atmospheric Particulate Matter Using the Materials Science Techniques XRD, FTIR, XRF, and Raman Spectroscopy DOI: 10.3390/su15118504 -
Nucleic acid confidence 1.0
“A positive band at 1682 was assigned to an RNA”
Correlations between autoantibodies and the ATR-FTIR spectra of sera from rheumatoid arthritis patients DOI: 10.1038/s41598-021-96848-w -
Acetate confidence 1.0
“Drugs N-C=O stretching 1682 and 1550 Clindamycin [32] C-O stretching 1038 and 1079 S-C-H bending”
Kravanja 和 Finsgar - 2021 - Analytical Techniques for the Characterization of DOI: 10.3390/biomedicines9121936
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