What absorbs at 1608 cm⁻¹ in an FTIR spectrum?
A band near 1608 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 1608 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 | 24 | 21 | 1.0 |
| Alkene (C=C) | 16 | 15 | 1.0 |
| Carboxyl (COOH) | 7 | 6 | 1.0 |
| C c single bond | 6 | 5 | 1.0 |
| Carbonyl (C=O) | 6 | 4 | 1.0 |
| Ring structure | 5 | 5 | 1.0 |
| Alkyl C-H | 5 | 4 | 1.0 |
| N h | 4 | 4 | 1.0 |
| Amide | 4 | 3 | 1.0 |
| Methacrylate | 4 | 3 | 1.0 |
| Acetate | 3 | 2 | 1.0 |
| Hydroxyl (O-H) | 3 | 2 | 1.0 |
| C-O single bond | 2 | 2 | 1.0 |
| Ketone | 2 | 1 | 1.0 |
| Ester | 2 | 1 | 1.0 |
| Silicon-oxygen (Si-O) | 2 | 1 | 1.0 |
| Protein | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| Methoxy (OCH3) | 1 | 1 | 1.0 |
| Protein beta sheet | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| Chitosan | 1 | 1 | 1.0 |
| Urethane | 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 |
|---|---|---|---|
| epoxy resin | 1608, 905, 1100 | Aromatic ring | 1 |
| graphene oxide | 1608, 1150, 3400 | 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 1608 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
-
Alkene (C=C) confidence 1.0
“In both cases the characteristic absorption bands are showed: 1509 and 1608 cm-1 (C=C bonds of aromatic ring), 1457 cm-1 (CH2 group vibration), 1362 cm-1 (methyl group vibration) and”
Barbadillo 等 - 2003 - Study of a curing reaction of an epoxy resin DOI: 10.4028/www.scientific.net/MSF.426-432.2163 -
confidence 1.0
“The Raman spectra 29 licensed cm(cid:1)1 cm(cid:1)1, on and 1350 corresponding to G presented characteristic peaks of graphene oxide at 1608 Published Si-O identified and D bands, respectively.”
Specific capture of glycosylated graphene oxide by an asialoglycoprotein receptor: a strategic approach for liver-targeting DOI: 10.1039/c8ra09732a -
Alkene (C=C) confidence 1.0
“peaks at 1608 and 1646 Both peaks can be assigned to carbon-carbon double bond stretching, the cm(cid:2)1 peak at 1608 arising from a carbon-carbon double bond of an aromatic ring and the peak at 1646 cm(cid:2)1 arises from the alkene group”
Fox 等 - 2004 - Investigation of failure mechanisms in aged aerosp DOI: 10.1016/j.engfailanal.2003.05.010 -
Carbonyl (C=O) confidence 1.0
“At 1735 isolate and chitosan coacervates by increasing the pH of cm-1, formation, due probably to the rising of the pH above the pI and 1608 stretching absorption bands of carbonyl (C=O) groups present in esterified carboxylic acid groups o”
Garcia-de la Rosa 等 - 2023 - Rheological and structural properties of complex c DOI: 10.24275/rmiq/Alim3003 -
Alkene (C=C) confidence 1.0
“their C=C absorption peaks at 1608 and 1522 Flour from the outer part of the kernel (corneous endosperm) had greater Pearson's protein and lipid absorbance while the inner kernel (floury endosperm) had stronger starch absorbance.”
Qualitative and Quantitative Analysis of Sorghum Grain Composition Including Protein and Tannins Using ATR-FTIR Spectroscopy DOI: 10.1007/s12161-020-01874-5 -
C c single bond confidence 1.0
“Text: 'dominant peaks at 3327 and 1608 ... (C--C, C--O)'”
Maimulyanti 等 - 2019 - Adsorption and recovery of aroma compounds from wa DOI: 10.2306/scienceasia1513-1874.2019.45.446 -
C c single bond confidence 1.0
“The percentage of unreacted carbon double bonds (% C=C) was determined from the ratio of absorbance -1 intensities of aliphatic C=C (peak at 1638 cm ) against an internal standard before and after the curing of the ° -1 specimen: aromatic C”
Rastelli 等 - 2008 - Degree of Conversion and Temperature Increase of a DOI: 10.1134/S1054660X0812030X -
C c single bond confidence 1.0
“The percentage of unreacted carbon-carbon double bonds (% C=C) was determined from the ratio of the absorbance -1 intensities of aliphatic C=C (peak at 1638 cm ) against an internal standard before and after the curing of the -1 specimen: a”
Rastelli 等 - 2008 - Effect of power densities and irradiation times on DOI: 10.1134/S1054660X08090132
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