What absorbs at 1780 cm⁻¹ in an FTIR spectrum?
A band near 1780 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 1780 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) | 18 | 14 | 1.0 |
| Carboxyl (COOH) | 9 | 7 | 1.0 |
| Amide | 8 | 6 | 1.0 |
| Ester | 7 | 5 | 1.0 |
| Methacrylate | 6 | 4 | 1.0 |
| Ketone | 6 | 4 | 1.0 |
| Acetate | 6 | 4 | 1.0 |
| Anhydride | 3 | 3 | 1.0 |
| Alkyl C-H | 2 | 2 | 1.0 |
| Protein | 2 | 2 | 1.0 |
| Ring structure | 2 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| Imide | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Lipid | 1 | 1 | 1.0 |
| Phospholipid | 1 | 1 | 0.8 |
| Alkene (C=C) | 1 | 0 | 1.0 |
| Metal oxygen | 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 |
|---|---|---|---|
| Polyurethanes | 1780, 1740, 1728 | Amide, Carbonyl (C=O), Ester | 1 |
| polystyrene | 1780, 1020, 1600 | Carbonyl (C=O), Amide | 1 |
| polyimide | 1780, 1720, 1778 | Amide, Carbonyl (C=O), 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 1780 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
-
Lipid confidence 1.0
“LLM confirmed rule peak-group candidate”
Depciuch 和 Parlinska-Wojtan - 2018 - Comparing dried and liquid blood serum samples of DOI: 10.1016/j.jpba.2017.11.074 -
Carbonyl (C=O) confidence 1.0
“cm(cid:3)1 bands at 1780 and 1857 with appearance of a new The ester carbonyl bond was deconvoluted to find out the cm(cid:3)1 carbonyl band at (cid:2)1730 assigned to ester and carboxdifferent ester groups formed by the reaction of anomeri”
Galgali 等 - 2007 - Sugar-linked biodegradable polymers Regio-specifi DOI: 10.1016/j.carbpol.2006.06.035 -
Anhydride confidence 1.0
“Two small peaks at 1780 and 1856cm-' are cyclic anhydride peaks caused by the BTDA, which is present in a slight stoichiometric excess 17 LIQUID CRYSTAL ALIGNMENT A b S 0 r b a n 2014 C e October 1200 1400 1800 1600 1000 28 W ers avenumb 05”
Ha 等 - 1998 - Polarized Infrared Spectroscopic Studies of Polari DOI: 10.1080/10587259808025380 -
Carboxyl (COOH) confidence 1.0
“The peaks at 2858 and 2956 cm-1 in the presence of O-H acid are found in Figures 4 Thepeaksat2858and2956cm-1 The peaks at 2858 and 2956 cm-1 in the presence of O-H acid are found in Figures 4 and 5, while carboxylic acid is found in the pea”
A Parametric Study on a Diesel Engine Fuelled Using Waste Cooking Oil Blended with Al2O3 Nanoparticle—Performance, Emission, and Combustion Characteristics DOI: 10.3390/su13137195 -
Protein confidence 1.0
“and (iv) the appearance of two IR bands According to Figure 5, the IR spectrum of protein G is dominated by two IR bands with maxima at 1699 and 1780 cm-1, both assigned to the C=O vibrational mode whose cm-1, at 1518 and 1634 which were as”
Optical Evidence for the Assembly of Sensors Based on Reduced Graphene Oxide and Polydiphenylamine for the Detection of Epidermal Growth Factor Receptor DOI: 10.3390/coatings11020258 -
Carbonyl (C=O) confidence 1.0
“observed in the carbonyl region of the IR spectrum of cm(cid:2)1 The high wavenumber feature, growing at 1780 PC (peak 60BM films exposed to light and air, can be assigned to two 1), is more difficult to assign because carbonyl peaks at hig”
Brumboiu 等 - 2022 - Photooxidation of PC60BM new insights from spectr DOI: 10.1039/d2cp03514f -
Amide confidence 1.0
“Infrared absorptions between 1780 and 1620 cm-1 indicated the presence of the carbonyl group (amide I), whereas bands 1550-1510 cm-1 ascribed deformation vibrations of N-H groups (amide II) and 1242-1240 cm-1 C-O stretching of the carbonate”
Branched Polyurethanes Based on Synthetic Polyhydroxybutyrate with Tunable Structure and Properties DOI: 10.3390/polym10080826 -
Carbonyl (C=O) confidence 1.0
“The FTIR cm-1, cm-1 spectra exhibited absorption bands of the imide rings at ~1780 and ~1720 attributed to the asymmetric and symmetric stretching vibration of the carbonyl group in the five-membered”
Azobenzene Functionalized “T-Type” Poly(Amide Imide)s vs. Guest-Host Systems— A Comparative Study of Structure-Property Relations DOI: 10.3390/ma13081912
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