What absorbs at 2868 cm⁻¹ in an FTIR spectrum?
A band near 2868 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 2868 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 | 12 | 12 | 1.0 |
| Methyl | 3 | 3 | 1.0 |
| Methoxy (OCH3) | 2 | 2 | 1.0 |
| Methacrylate | 2 | 2 | 1.0 |
| Acetate | 2 | 2 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Lipid | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| N h | 1 | 1 | 1.0 |
| Amide | 1 | 1 | 1.0 |
| Carboxyl (COOH) | 1 | 1 | 0.8 |
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 |
|---|---|---|---|
| Polypropylene | 2868, 1030, 1600 | Alkyl C-H, Methacrylate, Methoxy (OCH3) | 2 |
| chitosan | 2868, 1650, 1655 | Alkyl C-H, Methacrylate, Methoxy (OCH3) | 2 |
| TiO2 | 2868, 1700, 1093 | Alkyl C-H, Methacrylate, Methoxy (OCH3) | 1 |
| starch | 2868, 1650, 1540 | Methacrylate, Alkyl C-H, 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 2868 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
“rPP rPP + 10% -C-H (CH2) Vibrational Mode 2868.2 69.2 2870.0 70.9 2868.2 73.8 2868.2 83.2 WN Intensity WN Intensity WN Intensity WN Intensity stretching 1459.2 68.2 1459.3 70,6 1459.2 72,5 1459.3 80.1 C-O-H 2868.2 69.2 2870.0 70.9 2868.2 73”
Glass Powder Additive on Recycled Polypropylene Filaments: A Sustainable Material in 3D Printing DOI: 10.3390/polym14010005 -
Alkyl C-H confidence 1.0
“-NH2 (C-N Stretching) 2935.05cm-1 ±2935cm-1 Alkane(C-HStretching) (Medium) cm-1 cm-1 cm-1 and 2611.01 >3000 (Medium) Alkane (C-H Stretching) 2715.39 2879.43cm-1 and2868.32cm-1 ±2860cm-1 Alkane(C-HStretching) (Medium)”
Validation of the Developed Zero-Order Infrared Spectrophotometry Method for Qualitative and Quantitative Analyses of Tranexamic Acid in Marketed Tablets DOI: 10.3390/molecules26226985 -
Alkyl C-H confidence 1.0
“The bands appeared at 2868, 1272 and cm-1 1097 are attributed to the CH stretching, CH twisting 2”
Structural and electrical behaviours of amino acid-based solid polymer electrolytes DOI: 10.1007/s12034-021-02464-9 -
Alkyl C-H confidence 1.0
“cm-1) cm-1 are associated with stretching the symmetric (2939 According to literature reports, the peak at 1590 cm-1) and asymmetric (2868 methylene (CH 2) vibration in which is characteristic of amide I (NH bending vibrations) each compone”
Novel Starch/Chitosan/Aloe Vera Composites as Promising Biopackaging Materials DOI: 10.1007/s10924-020-01661-7 -
Alkyl C-H confidence 1.0
“LLM confirmed rule peak-group candidate”
Influence of the Heat Treatment on the Particles Size and on the Crystalline Phase of TiO2 Synthesized by the Sol-Gel Method DOI: 10.3390/ma11122364 -
Alkyl C-H confidence 1.0
“It was also observed a peak at 2905 and 2868 cm-1 related to CH 2.”
Gabriela Chuc-Gamboa 等 - 2021 - Antibacterial Behavior of Chitosan-Sodium Hyaluron DOI: 10.3390/app1103 -
Alkyl C-H confidence 1.0
“Precisely at 2868 a band of overlapping absorption corresponds cm-1, to CH.”
Valoration of the Synthetic Antioxidant Tris-(Diterbutyl-Phenol)-Phosphite (Irgafos P-168) from Industrial Wastewater and Application in Polypropylene Matrices to Minimize Its Thermal Degradation DOI: 10.3390/molecules28073163 -
confidence 1.0
“In the case of Au/TiO band characteristic of 2 2868cm-1, 2734-2764cm-1, 1556-1550cm-1 and adsorbed CO was not observed, or it was hardly detected.”
Kecskes 等 - 2004 - FTIR and mass spectrometric study of HCOOH interac DOI: 10.1016/j.apcata.2004.03.021
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