What absorbs at 1709 cm⁻¹ in an FTIR spectrum?
A band near 1709 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 1709 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 |
|---|---|---|---|
| Carbonyl (C=O) | 19 | 18 | 1.0 |
| Carboxyl (COOH) | 8 | 8 | 1.0 |
| Methacrylate | 7 | 7 | 1.0 |
| Acetate | 7 | 7 | 1.0 |
| Ester | 7 | 7 | 1.0 |
| Ketone | 5 | 5 | 1.0 |
| Amide | 5 | 5 | 1.0 |
| Lipid | 3 | 3 | 1.0 |
| Hydroxyl (O-H) | 3 | 3 | 1.0 |
| Methoxy (OCH3) | 2 | 2 | 1.0 |
| C-O single bond | 2 | 2 | 1.0 |
| Aromatic ring | 2 | 2 | 1.0 |
| Fatty acid | 1 | 1 | 1.0 |
| Aldehyde (CHO) | 1 | 1 | 1.0 |
| Alkyl C-H | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Metal oxygen | 1 | 1 | 1.0 |
| Alkene (C=C) | 1 | 1 | 1.0 |
| Carbohydrate | 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 |
|---|---|---|---|
| polyurethane | 1709, 2270, 1700 | Methacrylate, Acetate, Carbonyl (C=O) | 1 |
| polypyrrole | 1709, 1700, 400 | Methacrylate, Acetate, Carbonyl (C=O) | 1 |
| PEG | 1709, 1650, 1342 | Methacrylate, Acetate, Carbonyl (C=O) | 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 1709 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
-
Carbohydrate confidence 1.0
“In comparison to native cm-1 starch, the FTIR spectra of the starch-lipid complexes revealed one extra band at 1709 starch, the FTIR spectra of the starch-lipid complexes revealed one extra band at 1709 cm-1 (Figure 4).”
Formation of Intermediate Amylose Rice Starch–Lipid Complex Assisted by Ultrasonication DOI: 10.3390/foods11162430 -
Alkene (C=C) confidence 1.0
“ring),1547cm-1 stretching,1709cm-1,1706cm-1,1705cm-1 for (b), (c) due to C=C bond for (a),(b),(c) pyrrole 3161cm-1 (a),3399cm-1 3127cm-1for (b),3362cm-1 3128cm-1 respectively due to C=N stretching, for and and for (c) are assigned to the pr”
Synthesis, characterization, morphological and electrical studies of polypyrrole nanostructures DOI: 10.1063/1.5093829 -
Hydroxyl (O-H) confidence 1.0
“Three peak intensity bands of C= O stretching of ester at 1709 cm-1, O-H stretching of hydroxyl group at 3400 cm-1, and C-H stretching cm-1 vibration at 2942 were observed and related to polimerization of shellac.”
Khairuddin 等 - 2016 - FTIR studies on the effect of concentration of pol DOI: 10.1088/1742-6596/776/1/012053 -
Ester confidence 1.0
“Ester C=O Stretching Lipid 1709 Carboxyl C=O Stretching”
Qualitative and Quantitative Analysis of Sorghum Grain Composition Including Protein and Tannins Using ATR-FTIR Spectroscopy DOI: 10.1007/s12161-020-01874-5 -
Hydroxyl (O-H) confidence 1.0
“βCD peak at 1709 A broad peak due to stretching vibration of the OH groups in was”
Improvement of stability due to a cyclamen aldehyde/β-cyclodextrin inclusion complex DOI: 10.1016/j.molstruc.2020.128161 -
Hydrogen bond confidence 1.0
“to estimated the degree of phase separation in segmented PU.The formation of hydrogen bonding by -C=O group can be determined by examining the peak position at 1709 cm-1 cm-1 for hydrogen bonded -C=O and at 1731 for free -C=O.”
Suryani 和 Zaimahwati - 2014 - Fourrier Transform Infrared and Gel Permeation Chr DOI: 10.4028/www.scientific.net/AMM.525.162 -
Lipid confidence 1.0
“2 cm-1 C=O, the wave number at 1709 was the stretching vibrations of indicative of cutin and wax;”
Xu 等 - 2019 - Biological Effects of High-Voltage Electric Field DOI: 10.3390/app9183829 -
Carbonyl (C=O) confidence 1.0
“shows only one band localized at 1709 When PVPh is added progressively, the carbonyl stretching band observed of pure PVMK shifted slightly to a lower frequency, due to the formation of hydrogen bonding between carboxylic and”
Miscibility and Hydrogen Bonding in Blends of Poly(4-vinylphenol)/Poly(vinyl methyl ketone) DOI: 10.3390/polym6112752
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