What absorbs at 1603 cm⁻¹ in an FTIR spectrum?
A band near 1603 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 1603 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 |
|---|---|---|---|
| Aromatic ring | 11 | 11 | 1.0 |
| Carboxyl (COOH) | 10 | 10 | 1.0 |
| Carbonyl (C=O) | 7 | 7 | 1.0 |
| Methacrylate | 6 | 6 | 1.0 |
| Acetate | 6 | 6 | 1.0 |
| Ring structure | 5 | 5 | 1.0 |
| Ketone | 5 | 5 | 1.0 |
| Ester | 5 | 5 | 1.0 |
| Amide | 5 | 5 | 1.0 |
| Alkene (C=C) | 4 | 4 | 1.0 |
| Alkyl C-H | 4 | 4 | 1.0 |
| C c single bond | 3 | 3 | 1.0 |
| Hydroxyl (O-H) | 2 | 2 | 1.0 |
| C-S single bond | 2 | 2 | 1.0 |
| Methoxy (OCH3) | 1 | 1 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| N-O bond | 1 | 1 | 1.0 |
| Aldehyde (CHO) | 1 | 1 | 1.0 |
| Amino acid | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| N h | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| C=n | 1 | 1 | 1.0 |
| Siloxane (Si-O-Si) | 1 | 1 | 1.0 |
| Silicon-oxygen (Si-O) | 1 | 1 | 1.0 |
| Oxygen heterocycle | 1 | 1 | 0.8 |
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 |
|---|---|---|---|
| lignin | 1603, 1035, 1510 | Methacrylate, Aromatic ring | 1 |
| polypropylene | 1603, 1030, 1600 | Methacrylate, Carbonyl (C=O) | 1 |
| calcite | 1603, 2850, 2864 | Methacrylate | 1 |
| apatite | 1603, 3053, 1640 | 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 1603 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
-
Alkyl C-H confidence 1.0
“LLM confirmed rule peak-group candidate”
Fossil cutin of Macroneuropteris scheuchzeri (Late Pennsylvanian seed fern, Canada) DOI: 10.1016/j.coal.2012.10.012 -
Hydroxyl (O-H) confidence 1.0
“A cm-1 stretching modes of the C-H bonds of methyl groups (-CH 3), the broad band at 3400 results from the presence of -OH groups, and three major peaks reveals at around 1603, 1413 and 1023 cm-1.”
Rafe 和 Razavi - 2015 - Effect of Thermal Treatment on Chemical Structure DOI: 10.1080/10942912.2014.999864 -
C c single bond confidence 1.0
“parameters,10,16 humidity,7 intensity of the in-plane ring bending (low intensity) and the physical stresses such as cm-1 temperature,7 stress.23,24 vibrational band at 1630 was lower than the in-plane ring and mechanical Fast drying method”
Worku 等 - 2014 - Drug-olymer Miscibility across a Spray Dryer A Ca DOI: 10.1021/mp4003943 -
confidence 1.0
“The absorption bands near 1603 and cm-1 in the peak for the Si-O-Si structure was located at 1097 cm-1 1507 corresponded to the aromatic summation absorption”
Zuo 等 - 2013 - Tribological Behavior of Phenolic Resin Composites DOI: 10.1080/10402004.2012.732197 -
Carbonyl (C=O) confidence 1.0
“The spectrum of the treated calcite mineral with SNLS cm-1, showed a new peak at 1603 related to the carbonyl group stretching vibration of cm-1.”
Abdel-Halim 等 - 2023 - Apatite-Calcite Flotation Separation Using Sodium DOI: 10.3390/min13070970 -
Aromatic ring confidence 1.0
“The intensity of aromatic C-H vibrations at 1603 cm-1, cm-1”
Microsoft Word - Zadeh_ Valorization of bagasse alkali lignin to water-soluble derivatives through chemical modification_AAM.docx DOI: 10.1016/j.rser.2016.10.082 -
C=n confidence 1.0
“This was confirmed by the appearcm-1 υCH=N γCH=N ance of new bands at 1660 and 1016 corresponding to the and of cm-1 the azomethine group [25] and by the bands at 1603 and 758 corresponding to the υC=N υC-S-C and of the thiazole ring [26,27”
Synthesis, Characterization and Biological Activities of New Schiff Base Compound and Its Lanthanide Complexes DOI: 10.3390/ph15040454 -
Alkene (C=C) confidence 1.0
“The peak cm-1 at 1603 was associated with C=C stretching vibration of the vinyl group, besides”
Alassod 等 - 2021 - PolypropyleneLigninPOSS Nanocomposites Thermal DOI: 10.3390/ma14143950
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