What absorbs at 2850 cm⁻¹ in an FTIR spectrum?
A band near 2850 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 2850 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 | 200 | 176 | 1.0 |
| Methacrylate | 19 | 19 | 1.0 |
| Acetate | 19 | 19 | 1.0 |
| Lipid | 16 | 15 | 1.0 |
| Methyl | 14 | 14 | 1.0 |
| Methoxy (OCH3) | 13 | 13 | 1.0 |
| Amide | 11 | 11 | 1.0 |
| Hydroxyl (O-H) | 10 | 10 | 1.0 |
| Carbonyl (C=O) | 10 | 10 | 1.0 |
| Carboxyl (COOH) | 10 | 10 | 1.0 |
| Ester | 10 | 9 | 1.0 |
| Ketone | 8 | 8 | 1.0 |
| Carbohydrate | 6 | 6 | 1.0 |
| Aromatic ring | 6 | 6 | 1.0 |
| Hydrogen bond | 5 | 5 | 1.0 |
| Alkene (C=C) | 5 | 5 | 1.0 |
| C-O single bond | 5 | 5 | 1.0 |
| Protein | 3 | 3 | 1.0 |
| N-O bond | 2 | 2 | 1.0 |
| N h | 2 | 2 | 1.0 |
| Water (H2O) | 2 | 2 | 1.0 |
| Chitosan | 1 | 1 | 1.0 |
| Sulfate (SO4) | 1 | 1 | 1.0 |
| Amine primary | 1 | 1 | 1.0 |
| Silicon-oxygen (Si-O) | 1 | 1 | 1.0 |
| Silicon (Si) | 1 | 1 | 1.0 |
| Fatty acid | 1 | 1 | 1.0 |
| Isocyanate | 1 | 1 | 1.0 |
| Lignin | 1 | 1 | 1.0 |
| Silicate | 1 | 1 | 1.0 |
| Oxygen heterocycle | 1 | 1 | 1.0 |
| Urea | 1 | 1 | 1.0 |
| Silicon carbon | 1 | 1 | 1.0 |
| Silanol (Si-OH) | 1 | 1 | 1.0 |
| Carbon dioxide | 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 |
|---|---|---|---|
| Polystyrene | 2850, 1020, 1600 | Alkyl C-H, Methacrylate, Acetate | 1 |
| Polyethylene | 2850, 1737, 1720 | Alkyl C-H, Methacrylate, Acetate | 1 |
| hydroxyapatite | 2850, 1620, 1639 | Alkyl C-H, Methacrylate, Acetate | 1 |
| diamond | 2850, 1378, 1332 | Alkyl C-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 2850 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
“94(cid:5) 2955w 2954 C Hstretching C H 2850vw 1272+1583 2×1351 2709w 2×1195 2384vw”
Arjunan 等 - 2007 - Fourier transform infrared and Raman spectral assi DOI: 10.1016/j.saa.2006.09.044 -
Alkyl C-H confidence 1.0
“The bands between 2850 and 2959 indicate alkyl C-H (asymmetric of cm-1 and symmetric) stretching, while signals at 1556 indicate CH scissoring.”
Structural analysis and antioxidative properties of mutan (water-insoluble glucan) and carboxymethyl mutan from Streptococcus mutans DOI: 10.1016/j.procbio.2020.07.006 -
Alkyl C-H confidence 1.0
“Th e CH bands at 2930 and 2850 cm-1.”
Calderon 等 - 2011 - Chemical Differences in Soil Organic Matter Fracti DOI: 10.2136/sssaj2009.0375 -
Alkyl C-H confidence 1.0
“It was reported several peaks in the spectra in the region 2920 cm-1 and 2850 cm-1 assigned to symmetric and asymmetric C-H stretching of oleic acid.”
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 -
Carbohydrate confidence 1.0
“As the FA were added to the NK rice starch, the two new peaks at 2927 and 2850 cm-1 were seen.”
Formation of Intermediate Amylose Rice Starch–Lipid Complex Assisted by Ultrasonication DOI: 10.3390/foods11162430 -
Alkyl C-H confidence 1.0
“peaks were observed at 2850 and 2920 (cid:126)symmetric sp3 factors, such as grain size, grain boundary scattering, etc., However, no CH peaks and asymmetric at 3 TABLE I.”
Haque 等 - 1998 - Comparison of infrared, Raman, photoluminescence, DOI: 10.1063/1.367201 -
Alkyl C-H confidence 1.0
“Asymmetric and symmetric C-H stretching vibrations of CH and CH groups 2 3 cm-1 are associated with absorption bands at 2850 and 2920 [38].”
Hemeda 等 - 2021 - Synthesis of nanometer-sized PbZrxTi1-xO3 for gamm DOI: 10.1016/j.jpcs.2020.109688 -
Alkyl C-H confidence 1.0
“In addition, it was seen that the sludge had cm-1 a band at 2850.31 that corresponded to H-C-H stretching (alkyl, aliphatic).”
Hidayani 等 - 2022 - Acoustic and Mechanical Properties of Polystyrene DOI: 10.37358/Mat.Plast.1964
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.