What absorbs at 1746 cm⁻¹ in an FTIR spectrum?
A band near 1746 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 1746 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) | 26 | 22 | 1.0 |
| Acetate | 21 | 19 | 1.0 |
| Methacrylate | 20 | 18 | 1.0 |
| Amide | 19 | 16 | 1.0 |
| Ester | 19 | 15 | 1.0 |
| Carboxyl (COOH) | 18 | 15 | 1.0 |
| Ketone | 15 | 13 | 1.0 |
| Alkyl C-H | 7 | 5 | 1.0 |
| Methoxy (OCH3) | 5 | 5 | 1.0 |
| C-O single bond | 5 | 5 | 1.0 |
| Lipid | 2 | 2 | 1.0 |
| Alkene (C=C) | 2 | 2 | 1.0 |
| Fatty acid | 2 | 2 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| Protein | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| Silicon-oxygen (Si-O) | 1 | 1 | 1.0 |
| Silicon (Si) | 1 | 1 | 1.0 |
| N h | 1 | 1 | 1.0 |
| Methyl | 1 | 1 | 1.0 |
| Amino acid | 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 |
|---|---|---|---|
| silica | 1746, 1100, 1080 | Methacrylate, Acetate | 1 |
| pectin | 1746, 1150, 1735 | Methacrylate, Acetate, Amide | 1 |
| cellulose acetate | 1746, 1650, 1741 | Acetate, Carbonyl (C=O), Methacrylate | 1 |
| biodiesel | 1746, 858, 3470 | Carbonyl (C=O), Methacrylate, Acetate | 1 |
| alginate | 1746, 1100, 1715 | Methacrylate, Acetate, Amide | 1 |
| oil | 1746, 1161, 1163 | 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 1746 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
-
Ester confidence 1.0
“CO diesel is monitored by the ester stretch (1746 The impact of water on the precision of the biodiesel mixture is determined using a Karl Fischer titration to monitor water content.”
Ault 和 Pomeroy - 2012 - Quantitative Investigations of Biodiesel Fuel Usin DOI: 10.1021/ed101097n -
Carboxyl (COOH) confidence 1.0
“For free fatty acid (FFA) quantification, C=O cm-1 the band at 1708 was used, corresponding to the carboxylic acid, whereas for fatty acid cm-1 C=O methyl ester (FAME) quantification, the peak corresponding to at 1746 was considered, which”
Monitoring Enzymatic Hydroesterification of Low-Cost Feedstocks by Fourier Transform InfraRed Spectroscopy DOI: 10.3390/catal9060535 -
confidence 1.0
“5-FU-SPH In 5FU-SPH (Figure 4), the absorption frequencies of amino and carbonyl functionalities were observed at 3304 cm-1 and 1746 cm-1, respectively.”
Synthesis, Characterization, Theoretical and Experimental Anticancer Evaluation of Novel Cocrystals of 5-Fluorouracil and Schiff Bases against SW480 Colorectal Carcinoma DOI: 10.3390/pharmaceutics15071929 -
confidence 1.0
“Cellulose acetate intense yellow and red for the SSCA-A and SSCA-B, respectively, Silica sphere after38days.FTIRspectrashowmoreabsorptionat3478cm(cid:2)1corComposite respondingAOHstretchingvibration,at2963cm(cid:2)1causedbyACH Silica photol”
Kang - 2014 - Photoluminescence of cellulose acetate and silica DOI: 10.1016/j.spmi.2014.04.012 -
Carbonyl (C=O) confidence 1.0
“LLM confirmed rule peak-group candidate”
Nisinloaded alginatehigh methoxy pectin microparticles: preparation and physicochemical characterisation DOI: 10.1111/ijfs.12516 -
Carbonyl (C=O) confidence 1.0
“3 2 2 cm-1 peaks at 1746, 1655, 1547, and 1240 which were assigned to carbonyl compounds stretching) on the positive influence of PC1 loadings are supportive to distinguish MFR (α-helices), (partly pectin), protein amide I amide II, and (mo”
Specific Mycoparasite-Fusarium Graminearum Molecular Signatures in Germinating Seeds Disabled Fusarium Head Blight Pathogen’s Infection DOI: 10.3390/ijms22052461 -
Carbonyl (C=O) confidence 1.0
“In the range 1800(cid:2)1-1300cm(cid:2)1, of the characteristic absorption bands are the 1630cm(cid:2)1 peaks at 1746, assigned to the carbonyl and the peaks 1500cm(cid:2)1 at 1610, embodied to phenolic acid are both confirmed;”
Discrimination of different genuine Danshen and their extracts by Fourier transform infrared spectroscopy combined with two-dimensional correlation infrared spectroscopy DOI: 10.1016/j.saa.2012.06.013 -
Acetate confidence 1.0
“Stretching (asym) Vst -C--O 1746 (ester) Stretching Vst 2,CH 3)”
Fourier transform midinfrared spectroscopy evaluation of early stages of virgin olive oil autoxidation DOI: 10.1002/ejlt.201200317
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