What absorbs at 1609 cm⁻¹ in an FTIR spectrum?
A band near 1609 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 1609 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 |
|---|---|---|---|
| Amide | 12 | 11 | 1.0 |
| N h | 8 | 7 | 1.0 |
| Aromatic ring | 8 | 7 | 1.0 |
| Methacrylate | 6 | 6 | 1.0 |
| Carboxyl (COOH) | 6 | 6 | 1.0 |
| Acetate | 6 | 6 | 1.0 |
| Alkene (C=C) | 6 | 4 | 1.0 |
| Ring structure | 5 | 5 | 1.0 |
| C-O single bond | 4 | 4 | 1.0 |
| Ketone | 4 | 4 | 1.0 |
| Ester | 4 | 4 | 1.0 |
| Carbonyl (C=O) | 4 | 4 | 1.0 |
| Methoxy (OCH3) | 3 | 3 | 1.0 |
| Hydroxyl (O-H) | 3 | 2 | 1.0 |
| Amino acid | 3 | 2 | 1.0 |
| Lignin | 1 | 1 | 1.0 |
| C=n | 1 | 1 | 1.0 |
| Carbon bromine | 1 | 1 | 1.0 |
| Silicon-oxygen (Si-O) | 1 | 1 | 1.0 |
| Nitrogen heterocycle | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| Alkyl C-H | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| Protein alpha helix | 1 | 0 | 1.0 |
| Bromine | 1 | 0 | 1.0 |
| Hydrogen bond | 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 |
|---|---|---|---|
| MWCNT | 1609, 2876, 1430 | Methacrylate, Aromatic ring, N h | 1 |
| Polyamide | 1609, 1663, 1541 | Amide, Methacrylate, N h | 1 |
| Polyaniline | 1609, 1565, 1570 | Aromatic ring, Amide, Methacrylate | 1 |
| CS | 1609, 1645, 1720 | Methacrylate, Amide | 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 1609 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
-
confidence 1.0
“Explicit assignment: peak around 1609 shows characteristic of Pd-N interaction”
Highly Biological Active Antibiofilm, Anticancer and Osteoblast Adhesion Efficacy from MWCNT/PPy/Pd nanocomposite DOI: 10.1016/j.apsusc.2017.10.142 -
Aromatic ring confidence 1.0
“The degree of conversion (DC) of methacrylate dental resins is typically determined by spectroscopically measuring the decrease 1640cm(cid:2)1, ¼ ratioed before and after polymerization to an internal standard (aromatic ring of the vinyl (C”
Gauthier 等 - 2005 - A new method for quantifying the intensity of the DOI: 10.1016/j.biomaterials.2005.04.039 -
Aromatic ring confidence 1.0
“For instance, cm-1 the positive-going band peaking at 1609 has been attributed CAC in some studies to a disorder-induced aromatic ring stretching mode [18].”
Revisiting the Redox Transitions of Polyaniline. Semiquantitative Interpretation of Electrochemically Induced IR Bands DOI: 10.1016/j.jelechem.2021.115593 -
Acetate confidence 1.0
“However, with C=C and C-O stretching at 1609 peak were time, C-1 had significantly (p ≤ 0.05) lower ERV suggestive of saponins (Ahmad et al., 2013).”
Jairath 等 - 2023 - In vitro and in vivo evaluation of Prosopis cinera DOI: 10.47836/ifrj.30.2.06 -
Amide confidence 1.0
“Furthermore, the intensities of several peaks, the C O vibrations associated with the pyranose ring including The KAS method can be described by the following equation cm-1, cm-1 at 1166 the N H bending vibration at 1609 and the [30]:”
Study on the thermal degradation kinetics and pyrolysis characteristics of chitosan-Zn complex DOI: 10.1016/j.jaap.2016.03.021 -
confidence 1.0
“The band at 1609 is due to the amino acid of these spectra the region 1800-800 was divided into”
Structural analysis of some soluble elastins by means of FTIR and 2D IR correlation spectroscopy DOI: 10.1002/bip.21524 -
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 -
Amide confidence 1.0
“LLM confirmed rule peak-group candidate”
Tang 等 - 2009 - Effect of membrane chemistry and coating layer on DOI: 10.1016/j.desal.2008.04
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