What absorbs at 2875 cm⁻¹ in an FTIR spectrum?
A band near 2875 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 2875 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 | 24 | 22 | 1.0 |
| N h | 2 | 2 | 1.0 |
| Methacrylate | 2 | 2 | 1.0 |
| Acetate | 2 | 2 | 1.0 |
| Hydroxyl (O-H) | 2 | 2 | 1.0 |
| Lipid | 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 |
| Methoxy (OCH3) | 1 | 1 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Alkene (C=C) | 1 | 1 | 1.0 |
| Aldehyde (CHO) | 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 |
|---|---|---|---|
| Chitosan | 2875, 1650, 1655 | Alkyl C-H, Acetate, Methacrylate | 1 |
| polypropylene | 2875, 1030, 1600 | Alkyl C-H, Methacrylate, Acetate | 1 |
| glycerol | 2875, 1585, 1630 | Methacrylate, Acetate, 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 2875 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
“552 The characteristic signals of the CH stretching were detected at around 2875 The peaks”
Effect of glucose-induced Maillard reaction on physical, structural and antioxidant properties of chitosan derivatives-based films DOI: 10.1016/j.carbpol.2020.117341 -
Alkene (C=C) confidence 1.0
“LLM confirmed rule peak-group candidate”
Biomedical Grade Stainless Steel Coating of Polycaffeic Acid via Combined Oxidative and Ultraviolet Light-Assisted Polymerization Process for Bioactive Implant Application DOI: 10.3390/polym11040584 -
Hydroxyl (O-H) confidence 1.0
“P407 is characterised by principal peaks at 2875 (CH 1346cm(cid:3)1 1094cm(cid:3)1 might be explained by the equivalent cross-sectional surface area stretching), (OH bending) and (CO stretch-”
Al-Ani 等 - 2019 - The effect of the source and the concentration of DOI: 10.1016/j.jsps.2019.04.012 -
Alkyl C-H confidence 1.0
“Similar comments could be 268 applied to the asymmetric and symmetric stretching vibrations of C-H bonds at 2875 269”
Arrieta 等 - 2013 - Structure and mechanical properties of sodium and DOI: 10.1016/j.jfoodeng.2012.09.002 -
Alkyl C-H confidence 1.0
“The characteristic bands of PP (Figure 5) and R-PP (Figcm-1 cm-1 band at 2956 to the -CH stretching vibration and 2875 to the asymmetric -CH”
Cresnar 等 - 2021 - Insight into the Surface Properties of Wood Fiber- DOI: 10.3390/polym13101535 -
Acetate confidence 1.0
“As VeoVa shows the same functional between 2700 and 3100 cm-1 a spectral marker might be suggested, namely, a more progroups as the vinyl acetate monomer (C=O and C-O-C) but varies more significantly in a cm-1 nounced band at ~2875 cm-1 (Fi”
De Sa 等 - 2021 - Tracing Poly(Vinyl Acetate) Emulsions by Infrared DOI: 10.3390/polym13213609 -
Alkyl C-H confidence 1.0
“Moreover, the contribution associated to the cm-1 cm-1, variables belonging to the peak centered at 2875 and at (approximately) 3400 ascribable to the symmetrical and asymmetrical stretching of -C-H and of O-H, appears”
Foschi 等 - 2022 - Advanced Analytical Approach Based on Combination DOI: 10.3390/ph15060763 -
Alkyl C-H confidence 1.0
“(cm-1) Band Vibrations Peak (O-H stretch) 3400 (C-H stretch) 2875”
Gholami 等 - 2020 - Modification of Chitosan Membranes via Methane Ion DOI: 10.3390/molecules25102292
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