What absorbs at 2871 cm⁻¹ in an FTIR spectrum?
A band near 2871 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 2871 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 | 17 | 16 | 1.0 |
| Methacrylate | 3 | 3 | 1.0 |
| Acetate | 3 | 3 | 1.0 |
| Lipid | 2 | 2 | 1.0 |
| Methoxy (OCH3) | 2 | 2 | 1.0 |
| Phospholipid | 1 | 1 | 1.0 |
| Methyl | 1 | 1 | 1.0 |
| Fatty acid | 1 | 1 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| Chitosan | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Carboxyl (COOH) | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| Amide | 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 | 2871, 1650, 1655 | Alkyl C-H, Acetate, Methacrylate | 2 |
| epoxy | 2871, 1660, 1735 | Methacrylate, Acetate, Alkyl C-H | 1 |
| chitin | 2871, 1650, 1655 | 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 2871 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
“Schiff base ACCEPTED MANUSCRIPT 3.2 FTIR Spectral studies The Infra-red spectroscopic studies of 4EMP show three peaks around 2962, 2929 and 2871cm-1 which are characteristic of alkane homologues due to the CH 2CH functional 3”
Synthesis, crystal structures, quantum chemical studies and corrosion inhibition potentials of 4-(((4-ethylphenyl)imino)methyl)phenol and (E)-4-((naphthalen-2-ylimino) methyl) phenol Schiff bases DOI: 10.1016/j.molstruc.2017.06.104 -
Acetate confidence 1.0
“EWA-CH2 Group Symmetric Stretching ~2871 C=O Vibration Stretching ~1725 Polymers 2022, 14, x FOR PEER REVIEW 9 of 21”
Degradation Performance Investigation of Hydrothermally Stressed Epoxy Micro and Nanocomposites for High Voltage Insulation DOI: 10.3390/polym14061094 -
Alkyl C-H confidence 1.0
“But Figure 12(b) shows of -CH3 -C=N strong symmetric stretching mode peak of at 2871 cm-' and the -CH2 stretching mode peak at 2227 cm-' compared to the other stretching mode peaks.”
Ha 等 - 2001 - Spectroscopic stuides on the liquid crystal alignm DOI: 10.1080/10587250108028259 -
Alkyl C-H confidence 1.0
“The spectrum of cm(cid:0) 1 pure and cuminaldehyde-loaded gliadin fibers both had a ribbon-like cuminaldehyde showed distinctive peaks in the regions of 2930 (C-H morphology that might be attributed to the rapid evaporation of stretching vi”
Fabrication and characterization of cuminaldehyde-loaded electrospun gliadin fiber mats DOI: 10.1016/j.lwt.2021.111373 -
Hydroxyl (O-H) confidence 1.0
“2871cm-1 and OH stretching.”
Anusha 和 Fleming - 2016 - Synthesis and Characterization of Chitosan Nanoagg DOI: 10.1155/2016/5379424 -
Chitosan confidence 1.0
“In addition, in this study, XRD latus) and commercial chitosan showed bands at 2872 and cm-1, analysis of chitosan showed two peaks similar to those 2871 respectively, corresponding to the (CH 2) derived from organisms such as shrimp, crayf”
Characteristics of cricket (Gryllus bimaculatus) chitosan and chitosan-based nanoparticles DOI: 10.1007/s10068-018-0314-4 -
Acetate confidence 1.0
“1681 1685 C-O stretch 2871 2867 2868”
Eftimie 等 - 2017 - DFT Calculation of Vibrational Frequencies for Bet DOI: 10.1063/1.4972377 -
Alkyl C-H confidence 1.0
“cm-1 Ch peaks for were observed at 3328 (axial stretching of hydroxyl groups (O-H) H2SO4 cm-1 overlapped to the asymmetric/symmetric stretching of the amine bonds (N-H)), 2918 cm-1 cm-1 and 2871 ( C-H aliphatic stretching), 1652 (C=O stretc”
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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