What absorbs at 1604 cm⁻¹ in an FTIR spectrum?
A band near 1604 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 1604 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 |
|---|---|---|---|
| Carboxyl (COOH) | 13 | 13 | 1.0 |
| Aromatic ring | 13 | 13 | 1.0 |
| Methacrylate | 10 | 10 | 1.0 |
| Acetate | 10 | 10 | 1.0 |
| Amide | 10 | 9 | 1.0 |
| Carbonyl (C=O) | 9 | 7 | 1.0 |
| Ester | 7 | 7 | 1.0 |
| N h | 7 | 5 | 1.0 |
| Ketone | 6 | 6 | 1.0 |
| Alkene (C=C) | 6 | 5 | 1.0 |
| Hydroxyl (O-H) | 5 | 5 | 1.0 |
| Ring structure | 5 | 5 | 1.0 |
| Methoxy (OCH3) | 4 | 4 | 1.0 |
| C-O single bond | 4 | 4 | 1.0 |
| Secondary amine | 4 | 3 | 1.0 |
| Alkyl C-H | 3 | 3 | 1.0 |
| C c single bond | 3 | 3 | 1.0 |
| Protein | 2 | 2 | 1.0 |
| Amino acid | 2 | 2 | 1.0 |
| Urethane | 1 | 1 | 1.0 |
| Methyl | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| C=n | 1 | 1 | 1.0 |
| Ammonium | 1 | 1 | 1.0 |
| Lignin | 1 | 1 | 0.9 |
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 |
|---|---|---|---|
| Chitosan | 1604, 1650, 1655 | Acetate, Methacrylate | 1 |
| silica | 1604, 1100, 1080 | Methacrylate, Acetate | 1 |
| PLA | 1604, 1650, 1073 | Methacrylate, Acetate, 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 1604 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
“LLM confirmed rule peak-group candidate”
Chitosan Capped Copper Oxide Nanocomposite: Efficient, Recyclable, Heterogeneous Base Catalyst for Synthesis of Nitroolefins DOI: 10.3390/catal12090964 -
Aromatic ring confidence 1.0
“Peaks at wave number 1604 and 1456 indicated the vibration of the primary NH and the stretching vibration of C=C derived from aromatic ring,”
Enzymatic Synthesis of Bio-Surfactant Fructose Oleic Ester Using Immobilized Lipase on Modified Hydrophobic Matrix in Fluidized Bed Reactor DOI: 10.1016/j.aaspro.2016.02.150 -
N h confidence 1.0
“3 3345e 2O...H-NH 2) O of silica (Si with a weaker AS band at N-H bend (on Rh and silica) Pt/silicad 1606 1634 NH bend of NH on Rh (wide band) 1604 2 3”
Leewis 等 - 2006 - Ammonia adsorption and decomposition on silica sup DOI: 10.1016/j.apsusc.2005.12.115 -
N h confidence 1.0
“Peaks at 1604 and 1483 and related ∼20 All samples were sputter coated with a nm thick film of peaks are assigned to NH deformation bending modes of 2 Creative”
Magee 等 - 2023 - Silane functionalization of WS2 nanotubes for inte DOI: 10.1039/d3nr00583f -
C-O single bond confidence 1.0
“The peak at 1604 represents C-OH 233 cm-1 group of amides.”
Antibacterial, antibiofilm and cytotoxic effects of Nigella sativa essential oil coated gold nanoparticles DOI: 10.1016/j.micpath.2015.11.021 -
Aromatic ring confidence 1.0
“The three low frequency bands near 1604 and 1609 cm-1 do not contribute to the secondary structure and are related to aromatic side chain of amino acids cm-1.”
Sadat 和 Joye - 2020 - Peak Fitting Applied to Fourier Transform Infrared DOI: 10.3390/app10175918 -
C c single bond confidence 1.0
“The intense peak at 1604 stretching of the carbonyl cm(cid:0) C-- 1 C-C Sanna et al., 2014) each sample was dealcoholized and the pH adjusted and those at 1515 and 1447 are due to the stretching, -CH”
Characterization of the medium infrared spectra of polyphenols of red and white wines by integrating FT IR and UV–Vis spectral data DOI: 10.1016/j.lwt.2021.111604 -
Ammonium confidence 1.0
“1612 were observed for histidine in response to a temperature jump from 10 to 20 The lower cm-1 COOvibrational frequency at 1604 is assigned to the chain group which forms the intermolecular NH3+ cm-1 COOhydrogen bond with group, while the”
Ye 等 - 2007 - Intermolecular hydrogen bonds formed between amino DOI: 10.1088/1674-0068/20/04/461-467
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