What absorbs at 1669 cm⁻¹ in an FTIR spectrum?
A band near 1669 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 1669 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 | 7 | 6 | 1.0 |
| Carbonyl (C=O) | 4 | 4 | 1.0 |
| Carboxyl (COOH) | 3 | 3 | 1.0 |
| Methacrylate | 2 | 2 | 1.0 |
| Ketone | 2 | 2 | 1.0 |
| Ester | 2 | 2 | 1.0 |
| Acetate | 2 | 2 | 1.0 |
| Amine primary | 1 | 1 | 1.0 |
| Metal oxygen | 1 | 1 | 1.0 |
| Protein alpha helix | 1 | 1 | 1.0 |
| Protein beta turn | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| N h | 1 | 1 | 1.0 |
| Ammonium | 1 | 1 | 1.0 |
| Alkene (C=C) | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| C=n | 1 | 1 | 0.9 |
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 |
|---|---|---|---|
| Chitosan | 1669, 1650, 1655 | Amide, Methacrylate | 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 1669 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
“Both concanavalin A and cm-1 immunoglobulin G showed a major band at about 1669 (30% of the total amide I band), which was β-sheet assigned to secondary structures.”
Sadat 和 Joye - 2020 - Peak Fitting Applied to Fourier Transform Infrared DOI: 10.3390/app10175918 -
Carbonyl (C=O) confidence 1.0
“LLM confirmed rule peak-group candidate”
Preparation and Characterization of Polymer Membranes Impregnated with Carbon Nanotubes for Olive Mill Wastewater DOI: 10.3390/polym14030457 -
Acetate confidence 1.0
“υ The key FTIR spectral features of CFZ are (OH) phenolic coefficients 3423cm-1, 3297cm-1, The correlation were in the range from 0.9994 υ υ band at (NH) band at (CH) aromatic 3090cm-1, 2950cm-1, to 0.9996 for the studied drugs in pure form”
Ali 等 - 2017 - Solid-State FTIR Spectroscopic Study of Two Binary DOI: 10.1155/2017/5673214 -
Alkene (C=C) confidence 1.0
“The peak at 1669 cm-1 may be attributed to the C=C stretching vibrations [19].”
Quantification of the Geranium Essential Oil, Palmarosa Essential Oil and Phenylethyl Alcohol in Rosa damascena Essential Oil Using ATR-FTIR Spectroscopy Combined with Chemometrics DOI: 10.3390/foods10081848 -
Amide confidence 1.0
“All 0.98 (<0.01, CPC3) 2 represented, e.g., by the amide I and amide II bands at 1669 and Additional plant data Sweden <0.01 2 1540cm-1,respectively,tolipids,exemplifiedbyvibrationsat1156, Italy <0.01 3 Norway”
Combining Chemical Information From Grass Pollen in Multimodal Characterization DOI: 10.3389/fpls.2019.01788 -
confidence 1.0
“Adsorption Mechanism cm-1 cm-1, nitrogen adsorption, the position of the peak was shifted from 3332.82 to 3270.09 and the 1654cm-1 1669cm-1, The possible adsorption mechanism of ammonium nitrogen onto the CTS-ZMS surface can be”
Chitosan Modified Zeolite Molecular Sieve Particles as a Filter for Ammonium Nitrogen Removal from Water DOI: 10.3390/ijms21072383 -
Carbonyl (C=O) confidence 1.0
“(C=O) The amide I band originates from symmetric stretching vibrations of the carbonyl functional cm-1), β-turn α-helical group and indicates changes in anti-parallel sheets and (1688, 1681, 1669 cm-1), cm-1),”
Grunert 等 - 2020 - Vibrational Spectroscopy of Peritoneal Dialysis Ef DOI: 10.3390/biom10060965 -
Amide confidence 1.0
“cm-1 r DASH in H 2O (black line) and D 2O (green line) buffer look similar in the 1800-1350 M cm-1 region, but with a slight shift in the amide I region, reduced intensity at 1675 (+) and a n cm-1 newly appearing band at 1669 (-) (Figure 7a”
Iwata 等 - 2010 - Key Dynamics of Conserved Asparagine in a Cryptoch DOI: 10.1021/bi1009979.
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