What absorbs at 1618 cm⁻¹ in an FTIR spectrum?
A band near 1618 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 1618 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 |
|---|---|---|---|
| Alkene (C=C) | 10 | 9 | 1.0 |
| Carboxyl (COOH) | 7 | 7 | 1.0 |
| Hydroxyl (O-H) | 7 | 7 | 1.0 |
| N h | 6 | 6 | 1.0 |
| Aromatic ring | 6 | 6 | 1.0 |
| Protein beta sheet | 6 | 6 | 1.0 |
| Methacrylate | 5 | 5 | 1.0 |
| Acetate | 5 | 5 | 1.0 |
| Carbonyl (C=O) | 5 | 4 | 1.0 |
| Amide | 5 | 4 | 1.0 |
| Alkyl C-H | 4 | 4 | 1.0 |
| Methoxy (OCH3) | 4 | 4 | 1.0 |
| C-O single bond | 4 | 4 | 1.0 |
| C=n | 3 | 3 | 1.0 |
| Ketone | 2 | 2 | 1.0 |
| Ester | 2 | 2 | 1.0 |
| Secondary amine | 2 | 2 | 1.0 |
| Hydrogen bond | 2 | 2 | 1.0 |
| Water (H2O) | 2 | 2 | 1.0 |
| C c single bond | 2 | 1 | 1.0 |
| N-O bond | 2 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Silicon-oxygen (Si-O) | 1 | 1 | 1.0 |
| Protein random coil | 1 | 1 | 1.0 |
| Silanol (Si-OH) | 1 | 1 | 1.0 |
| Silicon (Si) | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Protein | 1 | 1 | 1.0 |
| Amino acid | 1 | 1 | 1.0 |
| N n bond | 1 | 1 | 1.0 |
| Fluorine (C-F) | 1 | 1 | 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 |
|---|---|---|---|
| chitosan | 1618, 1650, 1655 | Hydroxyl (O-H), N h | 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 1618 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
“The peaks at 1600 and 1618 cm-1 204 correspond to C=C stretching in aromatic nuclei.”
Effect of polyaniline (PANI) on Poly(vinylidene fluoride-co-hexaflouro propylene) (PVDF-co-HFP) polymer electrolyte membrane prepared by breath figure method DOI: 10.1016/j.polymertesting.2017.03.012 -
Protein beta sheet confidence 1.0
“lower cm-1) 26 intensity of the peak (1634 corresponding to native protein structural elements such as cm-1, cm-1 cm-1) 27 β-sheets intramolecular and higher intensities of peaks (1618 1683 and 1694”
Hempseed meal protein isolates prepared by different isolation techniques. Part I. physicochemical properties DOI: 10.1016/j.foodhyd.2017.12.015 -
Carboxyl (COOH) confidence 1.0
“Strong characteristic absorption peaks at 1618 assigned to 84 COOthe vibration of group of galacturonic acid.”
Lefsih 等 - 2016 - Extraction, characterization and gelling behavior DOI: 10.1016/j.ijbiomac.2015.10.046 -
N-O bond confidence 1.0
“The integrated band expected, the gas-phase NO and NO bands centered at 1618 2 2”
Mochida 和 Finlayson-Pitts - 2000 - FTIR study of N2O3 on porous glass at room tempera DOI: 10.1021/jp001484o -
confidence 1.0
“Medium peaks detected at 1617.72 and 1619.25 in the leaf and stem, respectively, corresponded to the N-H (bending) functional groups of primary”
Phytochemical Composition of Combretum molle (R. Br. ex G. Don.) Engl. & Diels Leaf and Stem Extracts DOI: 10.3390/plants12081702 -
Aromatic ring confidence 1.0
“cm-1 C-C of the neat TA spectrum, assigned to the 1618 stretching modes of aromatic rings, with possible contribution CO from the modes of H-bonded carbonyl groups (Figure 1c).”
Rivero 等 - 2012 - Heat Treatment To Modify the Structural and Physic DOI: 10.1021/jf204077k -
Hydrogen bond confidence 1.0
“The band around 1618 is also attributed to intermolecular with strong H-bonds [49].”
Sadat 和 Joye - 2020 - Peak Fitting Applied to Fourier Transform Infrared DOI: 10.3390/app10175918 -
Acetate confidence 1.0
“The absorption peaks cm-1 cm-1 at 1618 and 1044 can be attributed to C=O stretching of carbonyl groups and C-O-C symmetric cm-1 stretching, respectively.”
Synthesis and characterization of Gd3+-loaded hyaluronic acid-polydopamine nanoparticles as a dual contrast agent for CT and MRI scans DOI: 10.1038/s41598-023-31252-0
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