What absorbs at 2851 cm⁻¹ in an FTIR spectrum?
A band near 2851 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 2851 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 | 47 | 42 | 1.0 |
| Methacrylate | 6 | 6 | 1.0 |
| Acetate | 6 | 6 | 1.0 |
| Methyl | 4 | 4 | 1.0 |
| Methoxy (OCH3) | 4 | 4 | 1.0 |
| Amide | 4 | 4 | 1.0 |
| Lipid | 3 | 3 | 1.0 |
| Ketone | 2 | 2 | 1.0 |
| Ester | 2 | 2 | 1.0 |
| Carboxyl (COOH) | 2 | 2 | 1.0 |
| Carbonyl (C=O) | 2 | 2 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| N h | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| C=n | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| Phospholipid | 1 | 1 | 1.0 |
| C c single 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 |
|---|---|---|---|
| PVC | 2851, 834, 1195 | 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 2851 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
“Antioxidants 2022, 11, x FOR PEER REVIEW 11 of 16 CH (sp2) stretching 2918.92 cm-1 and 2851.05 cm-1 corresponding to the CH (sp3) stretch-”
The Effect of High-Intensity Ultrasound and Natural Oils on the Extraction and Antioxidant Activity of Lycopene from Tomato (Solanum lycopersicum) Waste DOI: 10.3390/antiox11071404 -
Alkyl C-H confidence 1.0
“(dcm-1, ) CH stretching band at 2932 the antisymmertic metal clusters, the ligand has a strong effect on the plasmon 2 cm-1,33,34 (d+) peak, as well, and in the case of MPC the optical spectra, are CH stretching modes at 2851 and symmetric”
Farrag 等 - 2012 - Preparation and Spectroscopic Properties of Monola DOI: 10.1021/jp210453v -
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 -
Aromatic ring confidence 1.0
“2 cm-1, 1493cm-1 and 2851 the aromatic ring vibrations at 1602 and cm-1 and the lines due to the CH deformation vibrations at 1452 2 (Kondyurin et al., 2008;”
60MeV Ni ion induced modifications in nano-CdS/polystyrene composite films DOI: 10.1016/j.radphyschem.2013.06.022 -
Water (H2O) confidence 1.0
“These ual water molecules are held tighter due to stronger interaction, 2851cm-1 for kaolinite band positions were located at 2920 and also confirmed by TG analysis.”
Li 等 - 2008 - An FTIR investigation of hexadecyltrimethylammoniu DOI: 10.1016/j.saa.2008.05.015 -
Alkyl C-H confidence 1.0
“LLM confirmed rule peak-group candidate”
Understanding Hydrothermal Dechlorination of PVC by Focusing on the Operating Conditions and Hydrochar Characteristics DOI: 10.3390/app7030256 -
Lipid confidence 1.0
“cm-1 α (related to RNA), 1651 (amide I helix structure), significant peak displacement were 1120 cm-1 cm-1 2851 (related to lipids - CH stretching) and 2962 (related to lipids - CH stretching).”
Mostaco-Guidolin 等 - 2010 - Molecular and chemical characterization by Fourier DOI: 10.3233/SPE-2010-0466 -
Alkyl C-H confidence 1.0
“LLM confirmed rule peak-group candidate”
Study on the Effect of Fe3+ on Zircon Flotation Separation from Cassiterite Using Sodium Oleate as Collector DOI: 10.3390/min7070108
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