What absorbs at 1729 cm⁻¹ in an FTIR spectrum?
A band near 1729 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 1729 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) | 35 | 27 | 1.0 |
| Ester | 16 | 13 | 1.0 |
| Methacrylate | 15 | 12 | 1.0 |
| Acetate | 15 | 12 | 1.0 |
| Carboxyl (COOH) | 14 | 11 | 1.0 |
| Amide | 13 | 9 | 1.0 |
| Ketone | 12 | 9 | 1.0 |
| C-O single bond | 5 | 5 | 1.0 |
| Methoxy (OCH3) | 4 | 4 | 1.0 |
| Hydroxyl (O-H) | 4 | 4 | 1.0 |
| Alkyl C-H | 2 | 2 | 1.0 |
| Urethane | 2 | 2 | 1.0 |
| Acetyl | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| Urea | 1 | 1 | 1.0 |
| Metal oxygen | 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.
Possible materials
| Material | Supporting peaks | Overlapping groups | Cited sources |
|---|---|---|---|
| polyester | 1729, 1700, 1250 | Carbonyl (C=O), Methacrylate, Acetate | 1 |
| TiO2 | 1729, 1700, 1093 | Methacrylate, Acetate | 1 |
| polyurethane | 1729, 2270, 1700 | 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 1729 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
-
Carbonyl (C=O) confidence 1.0
“Explicit assignment: 'The peak about 1729 cm-1 ... can be assigned to (C=O), the stretching mode of carbonyl groups'.”
Evaluation of microwave and magnetic properties of substituted SrFe12O19 and substituted SrFe12O19/multi-walled carbon nanotubes nanocomposites DOI: 10.1016/j.matchemphys.2013.08.045 -
Carbonyl (C=O) confidence 1.0
“The 15 (C]O) on carbonyl stretching appeared between 1729 and 1760cm(cid:2)1 Published whichincludestheestergroupfrom thePCLandthe”
Cetina-Diaz 等 - 2014 - Physicochemical characterization of segmented poly DOI: 10.1039/c3tb21500h -
Carbonyl (C=O) confidence 1.0
“cm-1 sample at 1729 and 1568 The peak at 1729 described a stretch vibration of the cm-1 C=O ester group, while the peak at 1568 showed an asymmetrical stretch vibration of the carboxyl group [6,50,51,66].”
Dual Modification of Sago Starch via Heat Moisture Treatment and Octenyl Succinylation to Improve Starch Hydrophobicity DOI: 10.3390/polym14061086 -
Urethane confidence 1.0
“LLM confirmed rule peak-group candidate”
Jana 等 - 2009 - Molecular Orientation of Polyurethane Based Liquid DOI: 10.1080/10601320903158719 -
Carbonyl (C=O) confidence 1.0
“This carbonyl peak at 1729 gradually decreased as cm-1 the DMT content increased.”
Synthesis, Characterization and Properties of Biodegradable Poly(Butylene Sebacate-Co-terephthalate) DOI: 10.3390/polym12102389 -
Acetate confidence 1.0
“peaks including aromatic C-H deformation at 670 cm-1, C-O stretching at 1052 cm-1, phenolic C-OH stretching at 1200 cm-1, C-OH at 1361 cm-1, hydroxyl groups of molecular water and C=C at 1625 cm-1, C=O stretching at 1729 cm-1, and a broad p”
Influence of Sputtering Temperature of TiO2 Deposited onto Reduced Graphene Oxide Nanosheet as Efficient Photoanodes in Dye-Sensitized Solar Cells DOI: 10.3390/molecules25204852 -
Hydroxyl (O-H) confidence 1.0
“For GNP, the peaks at 3439, 2925 can on the white zones which are indicative of the presence of be ascribed to the O H stretching, while the peaks at 1729, cm-1”
Phosphorization of exfoliated graphite for developing flame retardant ethylene vinyl acetate composites DOI: 10.1016/j.jmrt.2020.04.085 -
Acetate confidence 1.0
“The existence of peaks due to C=O and C-O cm-1 cm-1 stretching at 1729.1 and 1234.4 (Fig.”
Nurul 等 - 2012 - XRD, FTIR and C-13 CPMAS NMR Studies of Composite DOI: 10.4028/www.scientific.net/AMR.364.159
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