What absorbs at 2870 cm⁻¹ in an FTIR spectrum?
A band near 2870 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 2870 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 | 35 | 33 | 1.0 |
| Methyl | 9 | 7 | 1.0 |
| Methoxy (OCH3) | 7 | 7 | 1.0 |
| Methacrylate | 6 | 6 | 1.0 |
| Acetate | 6 | 6 | 1.0 |
| N h | 3 | 3 | 1.0 |
| Lipid | 3 | 3 | 1.0 |
| Secondary amine | 2 | 2 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| Amide | 1 | 1 | 1.0 |
| Protein | 1 | 1 | 1.0 |
| Carbonate | 1 | 1 | 1.0 |
| Fatty acid | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Sulfur | 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 |
|---|---|---|---|
| chitosan | 2870, 1650, 1655 | Alkyl C-H, Methacrylate, Methoxy (OCH3) | 2 |
| sodium alginate | 2870, 1636, 1080 | Alkyl C-H, Methacrylate, Methoxy (OCH3) | 1 |
| Nanocellulose | 2870, 1540, 1646 | Alkyl C-H, Methacrylate, Methoxy (OCH3) | 1 |
| chitin | 2870, 1650, 1655 | Alkyl C-H, Methacrylate, Methoxy (OCH3) | 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 2870 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
“The absorption band at around 2870 is ascribed to the asymmetric C-H cm-1 stretching, which is typical of polysaccharides.”
Aloe Vera extract-based composite nanofibers for wound dressing applications DOI: 10.1016/j.msec.2021.112061 -
Alkyl C-H confidence 1.0
“The alkane stretch C-H vibration between 2870 - cm-1.”
Fuel Analysis of Jatropha Methyl Ester and n-Tridecane as an Alternative Fuel for the Future DOI: 10.1051/matecconf/201815301002 -
Ring structure confidence 1.0
“COC Ar 2 asym Ar sym absorbance ring stretch 2870 1051 1457 2909 1604 1105”
Ready-to-Use Germanium Surfaces for the Development of FTIR-Based Biosensors for Proteins DOI: 10.1021/acs.langmuir.0c02681 -
Alkyl C-H confidence 1.0
“Similar C-H stretching vibrations near cm-1 2870 wavelength gave a peak in all samples except in GST”
Chaudhari 等 - 2015 - Fourier transform infrared analysis of Tamra Bhasm DOI: 10.4103/0974-8520.169013 -
Alkyl C-H confidence 1.0
“Due to the largest swelling degree cm-1 2870 is attributed to the stretch vibration of of CA2-1, composite hydrogels with attapulgite were -CH 2-.”
Chen 和 Hong - 2022 - Preparation of Chitin Composite Hydrogel for Dye-C DOI: 10.15244/pjoes/138210 -
Acetate confidence 1.0
“cm-1) ν in the intensity of signals in the high wavenumber (3050-2800 region, predominated by the as(CH 3), ν ν ν as(CH 2), s(CH 3) and s(CH 2) stretches arising from lipid species within the cell, and located at 2955, 2920, 2870 cm-1.”
Denbigh 等 - 2017 - Probing the action of a novel anti-leukaemic drug DOI: 10.1038/s41598-017-02069-5 -
Alkyl C-H confidence 1.0
“cm-1 cm-1 cm-1 and from 2870 characteristic to C-H stretching of -CH group and 2934 and 2844 3 C-H bond in -CH are strong in K_AT, which suggest the occurrence of new chain-ends due to the”
Bacterial Nanocellulose from Side-Streams of Kombucha Beverages Production: Preparation and Physical-Chemical Properties DOI: 10.3390/polym9080374 -
Hydroxyl (O-H) confidence 1.0
“The FTIR peaks for Acetic cm-1 cm-1 cm-1 were observed at 3421 (O-H and N-H stretching vibration), 2921 and 2870 cm-1”
Physicochemical Properties and Functional Characteristics of Ecologically Extracted Shrimp Chitosans with Different Organic Acids during Demineralization Step DOI: 10.3390/molecules27238285
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