What absorbs at 1765 cm⁻¹ in an FTIR spectrum?
A band near 1765 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 1765 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) | 7 | 7 | 1.0 |
| Carboxyl (COOH) | 4 | 4 | 1.0 |
| Methacrylate | 3 | 3 | 1.0 |
| Ketone | 3 | 3 | 1.0 |
| Ester | 3 | 3 | 1.0 |
| Amide | 3 | 3 | 1.0 |
| Acetate | 3 | 3 | 1.0 |
| Anhydride | 1 | 1 | 1.0 |
| N h | 1 | 1 | 1.0 |
Ranking reflects accumulated literature evidence, not a single authoritative rule. Always confirm against your sample context.
Possible materials
| Material | Supporting peaks | Overlapping groups | Cited sources |
|---|---|---|---|
| polypropylene | 1765, 1030, 1600 | Methacrylate, Carbonyl (C=O) | 1 |
| Polyester | 1765, 1700, 1250 | Carbonyl (C=O), Methacrylate | 1 |
| PLGA | 1765, 3200, 1741 | Carbonyl (C=O), Methacrylate | 1 |
| glycerol | 1765, 1585, 1630 | Methacrylate, Carbonyl (C=O), Carboxyl (COOH) | 1 |
| polyimide | 1765, 1720, 1778 | Carbonyl (C=O), Methacrylate, Carboxyl (COOH) | 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 1765 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
-
Carboxyl (COOH) confidence 1.0
“Polyethylene acid, phthylic acid, octadecatrienoic acid, acetic acid, samples oxidized when kept in oven for 10 days as hexanoic acid, octadeconoic acid, butanoic acid, oxamcm-1.(- indicated by the absorption band around 1765 imidic acid, u”
Biodegradation of thermally treated high-density polyethylene (HDPE) by Klebsiella pneumoniae CH001 DOI: 10.1007/s13205-017-0959-3 -
Carbonyl (C=O) confidence 1.0
“Explicit assignment in text.”
Formulation, optimization, and characterization of amlodipine besylate loaded polymeric nanoparticles DOI: 10.1177/09673911211056154 -
Acetate confidence 1.0
“The table peaks a strong C=O stretch of carboxylic (1765cm-1), (1625cm-1), also shows at which range of temperatures were certain acid monomers N-H bending in-”
Masite 等 - 2022 - Trace Metals, Crude Protein, and TGA-FTIR Analysis DOI: 10.1155/2022/1509569 -
Carbonyl (C=O) confidence 1.0
“Amide I (urea) 1690 1687 1680 C=O carbonyl stretching vibration (intensity less) 1765”
Rangel-Vazquez 等 - 2014 - Spectroscopy Analyses of PolyurethanePolyaniline DOI: 10.1590/0104-1428.1496 -
Acetate confidence 1.0
“In the next step, citraconic anhydride was observable by the band at 1840 cm-1 and 1765 cm-1 (C=O stretching of anhydride compounds) and 920 cm-1 (C-O stretching of the C-O-C) [43,44].”
Bio-Based Phosphate-Containing Polyester for Improvement of Fire Reaction in Wooden Particleboard DOI: 10.3390/polym15051093 -
Acetate confidence 1.0
“The peaks relevant to this study are highlighted in Figure 2, and the remaining combinations of 1.31-36 vibrational modes are represented by the dashed lines and summarized in Table It N should be noted that the unhydrolyzed acid chloride C”
Quantifying Carboxylic Acid Concentration in Model Polyamide Desalination Membranes via Fourier Transform Infrared Spectroscopy DOI: 10.1021/acs.macromol.8b01194. -
Carbonyl (C=O) confidence 0.9
“Well established with C=O.”
Mechanical and tribological characterization of CNx films deposited by d.c. magnetron sputtering DOI: 10.1002/pssc.200675911 -
confidence 0.9
“Explicit: 'bands initially present at 1695 and 1765 characteristic of PMDA C=O stretching'”
Innovative polypropylene based blends by in situ polymerization of a polyimide dispersed phase by reactive extrusion DOI: 10.1016/j.polymer.2022.125022
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