What absorbs at 1751 cm⁻¹ in an FTIR spectrum?
A band near 1751 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 1751 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) | 15 | 11 | 1.0 |
| Ester | 9 | 8 | 1.0 |
| Methacrylate | 8 | 7 | 1.0 |
| Acetate | 8 | 7 | 1.0 |
| Ketone | 7 | 6 | 1.0 |
| Carboxyl (COOH) | 7 | 6 | 1.0 |
| Amide | 7 | 6 | 1.0 |
| Alkyl C-H | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Protein | 1 | 1 | 1.0 |
| Triglyceride | 1 | 1 | 1.0 |
| Methoxy (OCH3) | 1 | 1 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| Alkene (C=C) | 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 |
|---|---|---|---|
| cellulose acetate | 1751, 1650, 1741 | Acetate, Carbonyl (C=O), Methacrylate | 1 |
| graphene | 1751, 1720, 2097 | Methacrylate, Acetate, Carbonyl (C=O) | 1 |
| edible oils | 1751, 1743, 1064 | Carbonyl (C=O), Ester, Methacrylate | 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 1751 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
“A small peak appears at 1751 indicates C=O”
Debataraja 等 - 2018 - Synthesis and Characterization of Nanocomposites o DOI: 10.22146/ijc.26660 -
Alkene (C=C) confidence 1.0
“Small intensity bands at 1751 cm(cid:1)1represent cm(cid:1)1represent C¼O and 1747 double bond of group whereas the peak at band 1639 the bending vibration of”
Role of iron in the enhanced reactivity of pulverized Red mud: Analysis by Mssbauer spectroscopy and FTIR spectroscopy DOI: 10.1016/j.cscm.2019.e00266 -
Acetate confidence 1.0
“We found that a broad cm-1, C=O band at 1751 ascribed to the stretching of the ester, appeared in the spectrum of RBE.”
Synthesis and Characterization of Novel Resveratrol Butyrate Esters That Have the Ability to Prevent Fat Accumulation in a Liver Cell Culture Model DOI: 10.3390/molecules25184199 -
Carbonyl (C=O) confidence 1.0
“Intensity ratio of the two carbonyl peaks I1751/I1709, corresponding to isolated and hydroless-oriented amorphous phase with respect to hydrogen-bonded HA dimer from the ε is particularly fast for form films exhibiting crystalline empty cha”
Monomeric and Dimeric Carboxylic Acid in Crystalline Cavities and Channels of Delta and Epsilon Forms of Syndiotactic Polystyrene DOI: 10.3390/polym13193330 -
Carbonyl (C=O) confidence 1.0
“Strong C=O absorption”
Du 等 - 2022 - Intraand Intermolecular Hydrogen Bonding in Misc DOI: 10.3390/ijms23137018 -
confidence 1.0
“the spectral band at 1751 can be attributed to an O-C-O”
Inerting Waste Al Alloy Dust with Natural High Polymers: Sustainability of Industrial Waste DOI: 10.3390/ma15165540 -
Ester confidence 1.0
“the single sharp peak at 1751 is due to the ester carbonyl functional group”
Hyperspectral Imaging and Chemometrics for Authentication of Extra Virgin Olive Oil: A Comparative Approach with FTIR, UV-VIS, Raman, and GC-MS DOI: 10.3390/foods12030429 -
Carbonyl (C=O) confidence 1.0
“the carbonyl stretching (μFTIR 1751 ATR-FTIR graphic reel from the outside to the inside, the μFTIR cm-1), cm-1;”
A diagnostic tool for assessing the conservation condition of cellulose nitrate and acetate in heritage collections: quantifying the degree of substitution by infrared spectroscopy DOI: 10.1186/s40494-020-00373-4
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