What absorbs at 1675 cm⁻¹ in an FTIR spectrum?
A band near 1675 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 1675 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 | 14 | 12 | 1.0 |
| Carbonyl (C=O) | 9 | 7 | 1.0 |
| Methacrylate | 8 | 8 | 1.0 |
| Acetate | 8 | 8 | 1.0 |
| Ketone | 5 | 5 | 1.0 |
| Ester | 5 | 5 | 1.0 |
| Carboxyl (COOH) | 5 | 5 | 1.0 |
| C-O single bond | 4 | 4 | 1.0 |
| Methoxy (OCH3) | 3 | 3 | 1.0 |
| N h | 2 | 2 | 1.0 |
| Ring structure | 2 | 2 | 1.0 |
| Alkyl C-H | 2 | 2 | 1.0 |
| Fatty acid | 1 | 1 | 1.0 |
| Amine primary | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Protein beta sheet | 1 | 1 | 1.0 |
| Oxygen heterocycle | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Alkene (C=C) | 1 | 1 | 1.0 |
| Aldehyde (CHO) | 1 | 1 | 0.9 |
| C c single bond | 1 | 0 | 1.0 |
| Protein alpha helix | 1 | 0 | 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 |
|---|---|---|---|
| lysozyme | 1675, 1560, 1640 | Amide, Methacrylate, Acetate | 1 |
| water | 1675, 1018, 2945 | Carbonyl (C=O), Methacrylate, Acetate | 1 |
| Sodium alginate | 1675, 1636, 1080 | 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 1675 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
-
Acetate confidence 1.0
“The peaks at 1675cm-1 1715 and belong to the C O stretching bands of”
Iwai 等 - 2006 - Measurement of entrainer effects of water and etha DOI: 10.1016/j.supflu.2005.12.005 -
Amide confidence 1.0
“All collected spectra are of amide I, and found that the band between 1675 and 1690 manipulated by GRAMS/AI 9.2 software, and the figures are cm-1 could be used for specific detection of Salmonella.”
Zhang 等 - 2021 - Influence of Hydrogen Bond and Sodium Alginate on DOI: 10.1016/S1872-2040(21)60101-9 -
Alkene (C=C) confidence 1.0
“cm-1 cm-1 is at 1718 The absorption peak at 1675 is C=C stretching, while 1636 is ascribed to the stretching vibration of the C=O in the conjugated carboxylic acid.”
HPTLC and FTIR Fingerprinting of Olive Leaves Extracts and ATR-FTIR Characterisation of Major Flavonoids and Polyphenolics DOI: 10.3390/molecules26226892 -
Alkyl C-H confidence 1.0
“FT-IR 3051 (C-H, s, stretching), 1675, 1635 (C=N, m, bending), 1597, 1471 (C=C, m, bending), 1158 (C-N, m,”
A Comprehensive Approach to Derivatization: Elemental Composition, Biochemical, and In Silico Studies of Metformin Derivatives Containing Copper and Zinc Complexes DOI: 10.3390/molecules28031406 -
Ring structure confidence 1.0
“LLM confirmed rule peak-group candidate”
Bertarione 等 - 2009 - Micro-FTIR and Micro-Raman Studies of a Carbon Fil DOI: 10.1021/jp9050534 -
Acetate confidence 1.0
“cm-1 The band around 1235 is likely from a -C-O vibration, and based on its position cm-1 and relative intensity towards the 1675 and 1545 bands, its origin is probably peptidic (amide III band) [31].”
Production of Exopolysaccharides by Cultivation of Halotolerant Bacillus atrophaeus BU4 in Glucose- and Xylose-Based Synthetic Media and in Hydrolysates of Quinoa Stalks DOI: 10.3390/fermentation8020079 -
Carbonyl (C=O) confidence 1.0
“LLM confirmed rule peak-group candidate”
Fabregat-Safont 等 - 2018 - Reporting the novel synthetic cathinone 5-PPDI thr DOI: 10.1007/s11419-013-0215-4 -
Protein beta sheet confidence 1.0
“assigned to β-sheet”
Frare 等 - 2006 - Identification of the core structure of lysozyme a DOI: 10.1016/j.jmb.2006.06.055
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