What absorbs at 1605 cm⁻¹ in an FTIR spectrum?
A band near 1605 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 1605 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 | 33 | 29 | 1.0 |
| Ring structure | 11 | 10 | 1.0 |
| Alkene (C=C) | 7 | 7 | 1.0 |
| Carbonyl (C=O) | 7 | 6 | 1.0 |
| C c single bond | 6 | 6 | 1.0 |
| Alkyl C-H | 6 | 6 | 1.0 |
| Methacrylate | 6 | 6 | 1.0 |
| Acetate | 6 | 6 | 1.0 |
| Carboxyl (COOH) | 5 | 5 | 1.0 |
| Lignin | 5 | 5 | 1.0 |
| N h | 4 | 4 | 1.0 |
| Methoxy (OCH3) | 4 | 4 | 1.0 |
| Amide | 4 | 4 | 1.0 |
| C=n | 3 | 3 | 1.0 |
| C-O single bond | 3 | 3 | 1.0 |
| Nitrogen heterocycle | 2 | 2 | 1.0 |
| Phosphate (PO4) | 2 | 2 | 1.0 |
| Hydroxyl (O-H) | 2 | 2 | 1.0 |
| Ketone | 2 | 2 | 1.0 |
| Ester | 2 | 2 | 1.0 |
| Lewis acid site | 2 | 2 | 1.0 |
| Ammonium | 1 | 1 | 1.0 |
| Lipid | 1 | 1 | 1.0 |
| Amino acid | 1 | 1 | 1.0 |
| Protein random coil | 1 | 1 | 1.0 |
| Protein beta sheet | 1 | 1 | 1.0 |
| Phosphorus | 1 | 1 | 1.0 |
| Amine primary | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| Methyl | 1 | 1 | 1.0 |
| Protein | 1 | 1 | 1.0 |
| Metal oxygen | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Phenolic | 1 | 1 | 0.7 |
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 |
|---|---|---|---|
| epoxy | 1605, 1660, 1735 | Carbonyl (C=O), Aromatic ring | 1 |
| biomass | 1605, 1082, 1282 | Aromatic ring | 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 1605 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
-
Amide confidence 1.0
“heated, the estimated ratio in the amide I region significantly cm-1 < Thus, the main peak at about 1605 for TA and SCT can (p 0.05) decreased from 1.49 in the untreated kafirin (control) 1.04-1.10 be assigned to aromatic rings.”
Byaruhanga 等 - 2006 - Alteration of kafirin and kafirin film structure b DOI: 10.1021/jf052942z -
C=n confidence 1.0
“LLM confirmed rule peak-group candidate”
Synthesis, crystal structures, quantum chemical studies and corrosion inhibition potentials of 4-(((4-ethylphenyl)imino)methyl)phenol and (E)-4-((naphthalen-2-ylimino) methyl) phenol Schiff bases DOI: 10.1016/j.molstruc.2017.06.104 -
Aromatic ring confidence 1.0
“~1725 Aromatic Ring C=C Stretching ~1605 Aromatic Ring C-C Stretching ~1506 Stretching of Symmetrical aromatic C-O-C”
Degradation Performance Investigation of Hydrothermally Stressed Epoxy Micro and Nanocomposites for High Voltage Insulation DOI: 10.3390/polym14061094 -
Alkene (C=C) confidence 1.0
“figure 5(b)), and also for the lignin associated C=C vibration aromatic ring at 1605 [20]”
Lim 和 Zulkifli - 2018 - Investigation of biomass surface modification usin DOI: 10.1088/2058-6272/aac819 -
Lewis acid site confidence 1.0
“remains above 473 K can most likely be attributed to the as- (cid:228) to 1288 while the peak at 1605 shifts to 1588 (NH 3) coordinated to Lewis acid sites that are still adsorbed on Both of these peaks remain, even as the temperature is in”
Pena 等 - 2004 - Identification of surface species on titania-suppo DOI: 10.1021/jp0313122 -
Ring structure confidence 1.0
“The bands at about 1605 and 1616 were present in all reference protein FT-Raman spectra (Figure 5) and correspond to the ring vibrations from aromatic residues.”
Sadat 和 Joye - 2020 - Peak Fitting Applied to Fourier Transform Infrared DOI: 10.3390/app10175918 -
Lewis acid site confidence 1.0
“As the temperature of hydrogen was strong ature of increased, metal species bonded to the non-acidic terminal silanol (SiOH) the intensity of the bands at 1605, 1585, 1460 and cm-1 groups 1385 and/or the bridging hydroxyl (SiOHAl) groups on”
IR study of iridium bonded to perturbed silanol groups of Pt-HZSM5 for n-pentane isomerization DOI: 10.1016/j.apcata.2011.12.039 -
Alkyl C-H confidence 1.0
“during the curing process and the appearance of band at polymerized monomers show the absorption bands at cm-1 1605 indicates the propargyl group is converted cm-1 and are assigned to the cyclohex(cid:2) 1018 and 941 ≡C-H into chromene stru”
Surender 等 - 2014 - Bismaleimide and Bispropargyl Ether Blends Curing DOI: 10.1134/S1560090414050157
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