What absorbs at 1730 cm⁻¹ in an FTIR spectrum?
A band near 1730 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 1730 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) | 151 | 128 | 1.0 |
| Ester | 97 | 90 | 1.0 |
| Carboxyl (COOH) | 92 | 85 | 1.0 |
| Methacrylate | 91 | 88 | 1.0 |
| Acetate | 91 | 88 | 1.0 |
| Amide | 78 | 74 | 1.0 |
| Ketone | 77 | 74 | 1.0 |
| Carbohydrate | 20 | 18 | 1.0 |
| C-O single bond | 19 | 19 | 1.0 |
| Alkyl C-H | 18 | 17 | 1.0 |
| Methoxy (OCH3) | 16 | 16 | 1.0 |
| Hydroxyl (O-H) | 11 | 9 | 1.0 |
| Acetyl | 9 | 9 | 1.0 |
| Alkene (C=C) | 7 | 6 | 1.0 |
| Aldehyde (CHO) | 6 | 6 | 1.0 |
| N h | 5 | 4 | 1.0 |
| Ring structure | 5 | 4 | 1.0 |
| Lignin | 3 | 2 | 1.0 |
| Aromatic ring | 3 | 2 | 1.0 |
| Nitrogen heterocycle | 2 | 2 | 1.0 |
| Water (H2O) | 2 | 2 | 1.0 |
| Methyl | 2 | 2 | 1.0 |
| C c single bond | 2 | 2 | 1.0 |
| Secondary amine | 2 | 1 | 1.0 |
| Lipid | 2 | 1 | 1.0 |
| C-S single bond | 1 | 1 | 1.0 |
| N-O bond | 1 | 1 | 1.0 |
| Ammonium | 1 | 1 | 1.0 |
| Phospholipid | 1 | 1 | 1.0 |
| Nitro (NO2) | 1 | 1 | 1.0 |
| Amine primary | 1 | 1 | 1.0 |
| N c o | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Urethane | 1 | 1 | 1.0 |
| Thiocarbonyl | 1 | 0 | 1.0 |
| Protein | 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 |
|---|---|---|---|
| graphene oxide | 1730, 1150, 3400 | Methacrylate, Carboxyl (COOH), 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 1730 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
“cm-1 The peak at 1730 was assigned to C=O stretching from unconjugated ketone, carbonyl, and origin63.”
Physicochemical characterisation of barley straw treated with sodium hydroxide or urea and its digestibility and in vitro fermentability in ruminants DOI: 10.1038/s41598-022-24738-w -
Acetate confidence 1.0
“51 52 cm-1, films displayed usually sharp C=O stretching peaks at 1730 but this peak was notably broader 53 2+ cm-1 54 2.”
Surface Grafting of Ru(II) Diazonium-Based Sensitizers on Metal Oxides Enhances Alkaline Stability for Solar Energy Conversion DOI: 10.1021/acsami.7b16641 -
Ring structure confidence 1.0
“The region cm-1, above 1730 where A-ring vibrations are located, is plotted with a 6× intensity scaling factor due to rel-”
Chenchiliyan 等 - 2023 - Ground-state heterogeneity and vibrational energy DOI: 10.1063/5.0135268 -
Aldehyde (CHO) confidence 1.0
“appearance of carboxylic acid and aldehyde peaks at 1730 and 3.1.”
Chu 和 Yaylayan - 2009 - FTIR monitoring of oxazolidin-5-one formation and DOI: 10.1016/j.carres.2008.10.011 -
Carboxyl (COOH) confidence 1.0
“The colloidal cm(cid:1)1 (C-O conjugation of GO, the band observed at 1730 dispersionisstablewhenaforcecausesthemutualrepulsionof is stretching peak for carboxylic acid) vanished, but it was also article particles.23 the In general, a parti”
Specific capture of glycosylated graphene oxide by an asialoglycoprotein receptor: a strategic approach for liver-targeting DOI: 10.1039/c8ra09732a -
Carboxyl (COOH) confidence 1.0
“The intensity of the aldehyde and acid peaks at 1730 and cm-1 21-23 Ag+ AgNO 1710 respectively were measured.”
A new approach to silver-catalysed aerobic oxidation of octadecanol: Probing catalysts utilising a flat, two-dimensional silicon-based model support system DOI: 10.1016/j.catcom.2012.07.013 -
Acetyl confidence 1.0
“Hemicelluloses were the first to degrade as proved by the initial decrease cm-1 of the 1730 peak due to the breaking of acetyl groups in xylan.”
Esteves 等 - 2013 - CHEMICAL CHANGES OF HEAT TREATED PINE AND EUCALYPT DOI: 10.4067/S0718-221X2013005000020 -
Carbonyl (C=O) confidence 1.0
“The Fourier transform infrared spectrum of the resin composite showed an inThis study was based on the preparation and comparative analysis of the mechanical, tense stretching peak at 1730 cm-1 corresponding to carbonyl groups (C=O), an ami”
Structural, Physical, and Mechanical Analysis of ZnO and TiO2 Nanoparticle-Reinforced Self-Adhesive Coating Restorative Material DOI: 10.3390/ma14247507
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