What absorbs at 2918 cm⁻¹ in an FTIR spectrum?
A band near 2918 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 2918 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 |
|---|---|---|---|
| Alkyl C-H | 64 | 60 | 1.0 |
| Hydroxyl (O-H) | 13 | 11 | 1.0 |
| Methacrylate | 10 | 10 | 1.0 |
| Acetate | 10 | 10 | 1.0 |
| Carboxyl (COOH) | 8 | 8 | 1.0 |
| Methyl | 8 | 8 | 1.0 |
| Methoxy (OCH3) | 6 | 6 | 1.0 |
| Amide | 6 | 6 | 1.0 |
| Lipid | 5 | 5 | 1.0 |
| Ester | 5 | 5 | 1.0 |
| C-O single bond | 5 | 4 | 1.0 |
| Carbohydrate | 4 | 4 | 1.0 |
| Ketone | 4 | 4 | 1.0 |
| Carbonyl (C=O) | 4 | 4 | 1.0 |
| N h | 4 | 4 | 1.0 |
| Fatty acid | 3 | 3 | 1.0 |
| Alkene (C=C) | 2 | 2 | 1.0 |
| Ring structure | 2 | 1 | 1.0 |
| Lignin | 1 | 1 | 1.0 |
| Urea | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| Amine primary | 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 |
|---|---|---|---|
| polyaniline | 2918, 1565, 1570 | Alkyl C-H, Methacrylate, Acetate | 1 |
| honey | 2918, 2005, 1199 | Methacrylate, Acetate, Alkyl C-H | 1 |
| cotton fabric | 2918, 900, 862 | Alkyl C-H, Methacrylate, Acetate | 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 2918 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
-
Alkyl C-H confidence 1.0
“propolis, two sharp peaks were observed at 2918 and n p 2851cm(cid:3)1, i¼1 corresponding to asymmetrical and symmetC-H groups in rical stretching vibrations of of CH "predicted" where refers to a value computed by the”
Cebi 等 - 2020 - An evaluation of FTIR spectroscopy for prediction DOI: 10.1080/00218839.2019.1707009 -
Alkyl C-H confidence 1.0
“The extra sharp asymmetric and symmetric C-H cotton fabric samples that were greige, water2849cm(cid:2)1 stretching peaks at 2918 and boiled, hexane-methanol extracted or incompletely in the 10 Textile Research Journal 0(00) 2.”
Characterization of cotton fabric scouring by Fourier transform-infrared attenuated total reflectance spectroscopy, gas chromatography-mass spectrometry and water absorption measurements DOI: 10.1177/0040517518790976 -
Alkyl C-H confidence 1.0
“The band at 2918 denoted the AC C-H stretching vibration of the alkane functional group, while the bands between 1000 and 800”
Mesoporous magnetite nanoparticles synthesis using the Peltophorum pterocarpum pod extract, their antibacterial efficacy against pathogens and ability to remove a pollutant dye DOI: 10.1016/j.molstruc.2018.10.042 -
Alkyl C-H confidence 1.0
“C-H stretching - - 2917.81 2917.81 2918 Asymmetric CH stretch 2”
Dave 等 - 2014 - The removal of impurities from gray cotton fabric DOI: 10.1080/00405000.2013.827900 -
Alkyl C-H confidence 1.0
“Explicit assignment in text”
Conversion of Sewage Water into H2 Gas Fuel Using Hexagonal Nanosheets of the Polyaniline-Assisted Deposition of PbI2 as a Nanocomposite Photocathode with the Theoretical Qualitative Ab-Initio Calculation of the H2O Splitting DOI: 10.3390/polym14112148 -
Alkyl C-H confidence 1.0
“O-H 3341 stretch Polysaccharides C-H 2918 vibration Polysaccharides 2851 CH stretch”
Modification of hemp shiv properties using water-repellent sol–gel coatings DOI: 10.1007/s10971-018-4621-2 -
Hydroxyl (O-H) confidence 1.0
“alcohol stretching 2917.81 medium C-H alkane”
Phytochemical Composition of Combretum molle (R. Br. ex G. Don.) Engl. & Diels Leaf and Stem Extracts DOI: 10.3390/plants12081702 -
C-O single bond confidence 1.0
“3299.09 3530.15 3565.78 C-H actions between the anti-Alzheimer's drugs (PC-37 and tacrine) Alkenyl stretching 2920.30 2918.84 2917.80 Open C-OH stretching 2848.72 2480.15 2849.57 and AIL (4-PyC8).”
Multi-spectroscopic monitoring of molecular interactions between an amino acid-functionalized ionic liquid and potential anti-Alzheimer's drugs DOI: 10.1039/d0ra06323a
Have a spectrum with this band?
Upload your FTIR spectrum and get a full interpretation report — peak assignments with literature citations, library matches, and a literature-backed analysis — in seconds.