What absorbs at 2908 cm⁻¹ in an FTIR spectrum?
A band near 2908 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 2908 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 |
| Hydroxyl (O-H) | 3 | 3 | 1.0 |
| Aromatic ring | 2 | 2 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| N h | 1 | 1 | 1.0 |
| Alkene (C=C) | 1 | 1 | 1.0 |
| Lignin | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| Chitosan | 1 | 1 | 1.0 |
| Silicon carbon | 1 | 1 | 0.6 |
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 |
|---|---|---|---|
| PVA | 2908, 1660, 2930 | Alkyl C-H, Hydroxyl (O-H) | 1 |
| cellulose | 2908, 1735, 1650 | Alkyl C-H, Hydroxyl (O-H) | 1 |
| PLA | 2908, 1650, 1073 | Alkyl C-H, Hydroxyl (O-H) | 1 |
| MWCNTs | 2908, 3396, 1735 | Alkyl C-H, Hydroxyl (O-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 2908 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
-
Chitosan confidence 1.0
“The peak at 2908.04 corresponded to cm(cid:2)1 Chitosan film CeH the stretching, while the band at 1335.74 was OeH the of water.”
Bourtoom 和 Chinnan - 2008 - Preparation and properties of rice starch-chitosan DOI: 10.1016/j.lwt.2007.10.014 -
Hydroxyl (O-H) confidence 1.0
“The strong 3421 peaks in Figures 1A and 3481 in cm-1 Figure 1B relates to the O-H region and the peaks at 2908 (Figure 1A) and 2900 (Figure 1B) are associated with the C-H stretching vibrations (Poletto et al.”
Daniel 等 - 2020 - Citric acid modified cellulose a cost effective a DOI: 10.1080/15567036.2020.1773963 -
Alkyl C-H confidence 1.0
“to C-H asymmetric stretching vibration takes place at 2908 For the doped samples, there is an evident cm-1, shift and significant decline in this band.”
Tea from the drinking to the synthesis of metal complexes and fabrication of PVA based polymer composites with controlled optical band gap DOI: 10.1038/s41598-020-75138-x -
Alkyl C-H confidence 1.0
“C-H asymmetric stretching vibration is associated with a band at 2908 [33], which also in the case of the doped samples is shifted to smaller wave numbers.”
From Green Remediation to Polymer Hybrid Fabrication with Improved Optical Band Gaps DOI: 10.3390/ijms20163910 -
Alkyl C-H confidence 1.0
“0.08 C=O stretching vibrations 1720.19 1747.19 C-H stretch (aromatic ring) 2908.13 2908.13 0.1 2927.41 C-H stretch (aromatic ring)”
Goldson Barnaby 等 - 2016 - Characterization of Jamaican Delonix regia and Cas DOI: 10.1155/2016/3850102 -
Hydroxyl (O-H) confidence 1.0
“In the OPEFB FTIR spectrum, broadband is observed at 2908 and 1760 respectively, which represents -OH stretching vibration of cellulose, hemicellulose, and lignin.”
The Effect of MWCNTs Filler on the Absorbing Properties of OPEFB/PLA Composites Using Microstrip Line at Microwave Frequency DOI: 10.3390/ma13204581 -
Alkyl C-H confidence 1.0
“3308 3305 Attributions SPMC_0 SPMC_1 SPMC_2 C-H stretching 2908 2915 2916”
Polymer Composites with 0.98 Transparencies and Small Optical Energy Band Gap Using a Promising Green Methodology: Structural and Optical Properties DOI: 10.3390/polym13101648 -
Alkyl C-H confidence 1.0
“The positive values of PC1 loading in the lipid region (Figure 4B) at 2969 cm-1 (assigned H-CO), to νas of 2941 cm-1 (νas of CH3 [27]), 2908 cm-1 (assigned to νs of CH2 and CH3 of lipid [28]), (C-H 2865 cm-1 stretching [29]), and 2838 cm-1”
FTIR Microspectroscopy for the Assessment of Mycoplasmas in HepG2 Cell Culture DOI: 10.3390/app10113766
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