What absorbs at 1667 cm⁻¹ in an FTIR spectrum?
A band near 1667 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 1667 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 | 9 | 1.0 |
| Carbonyl (C=O) | 8 | 8 | 1.0 |
| Methacrylate | 6 | 6 | 1.0 |
| Acetate | 6 | 6 | 1.0 |
| Ester | 6 | 6 | 1.0 |
| Ketone | 5 | 5 | 1.0 |
| Carboxyl (COOH) | 5 | 5 | 1.0 |
| Hydroxyl (O-H) | 4 | 4 | 1.0 |
| Methoxy (OCH3) | 2 | 2 | 1.0 |
| C-O single bond | 2 | 2 | 1.0 |
| Secondary amine | 2 | 2 | 1.0 |
| C n single bond | 2 | 2 | 1.0 |
| Alkyl C-H | 2 | 2 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Protein alpha helix | 1 | 1 | 1.0 |
| Protein beta sheet | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Lipid | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| Aromatic ring | 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 |
|---|---|---|---|
| chitosan | 1667, 1650, 1655 | Amide, Acetate, Methacrylate | 1 |
| chitin | 1667, 1650, 1655 | Amide, Methacrylate, Acetate | 1 |
| quercetin | 1667, 1745, 1612 | 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 1667 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
-
Ester confidence 1.0
“The peak at 1745 is the peak vibration of ester bond - 1667 This assessment is not so obvious when these carbonyl stretching and appears discreetly in AND.”
Martins 等 - 2019 - Approach by Raman and infrared spectroscopy in thr DOI: 10.31349/RevMexFis.65.328 -
confidence 1.0
“cm-1 CN al.48 Aregahegn et attributed the 1667 peak to the”
Probing Matrix Effects on the Heterogeneous Photochemistry of Neonicotinoid Pesticides, Dinotefuran and Nitenpyram DOI: 10.1021/acsearthspacechem.1c00059 -
Hydroxyl (O-H) confidence 1.0
“In the cm-1 FTIR spectrum of Qu, absorbance at 3411 was cm-1 assigned to a free -OH bond vibration,at 1667 and cm-1 1612 were assigned to the stretching vibration of”
Setyawan 等 - 2018 - Improvement in vitro Dissolution Rate of Quercetin DOI: 10.22146/ijc.28511 -
Amide confidence 1.0
“differences in crystalline peaks between α, β and γ chitins obtained from various sources The cm-1, suggests that chitin extracted Amide I band is split at 1667 which indicates that this chitin from P.”
Chitin and Chitosan preparation from shrimp shells Penaeus monodon and its human Ovarian Cancer Cell Line, PA-1 DOI: 10.1016/j.ijbiomac.2017.09.035 -
Amide confidence 1.0
“cm-1 t Since the Amide I peak at 1667 is weak compared to the predominant phosphate peak h o cm-1 cm-1 at ~ 960 or other organic peaks such as the CH 2-wag at 1453 (Fig.”
Assessing Glycation-mediated Changes in Human Cortical Bone with Raman Spectroscopy DOI: 10.1002/jbio.201700352. -
Amide confidence 1.0
“LLM confirmed rule peak-group candidate”
Ligand Radical Mediated Water Oxidation by a Family of Copper o -Phenylene Bis-oxamidate Complexes DOI: 10.1021/acs.inorgchem.1c00546 -
Water (H2O) confidence 1.0
“The occurrence of 1667cm-1 well-resolved water bending vibration bands at about 1595 and accounts for more than one structural water molecule as expected by charoite-90 polytype structure model from literature.”
Lacalamita - 2018 - Micro-FTIR and EPMA Characterisation of Charoite f DOI: 10.1155/2018/9293637 -
Hydroxyl (O-H) confidence 1.0
“The characteristic peaks at ~3424 cm-1, 2860-2925 cm-1, ~1667 cm -1, ~1240 cm and 1281 cm which belong to O-H, C-H, C=O, C-O and C-N bond vibrations respec- -1 -1, tively in the PVP modified GO, can also be seen in the GO@AuNRs.”
Graphene Oxide-Gold Nanorods Nanocomposite-Porphyrin Conjugate as Promising Tool for Cancer Phototherapy Performance DOI: 10.3390/ph14121295
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