What absorbs at 2951 cm⁻¹ in an FTIR spectrum?
A band near 2951 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 2951 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 | 15 | 13 | 1.0 |
| Methyl | 7 | 6 | 1.0 |
| Methoxy (OCH3) | 6 | 6 | 1.0 |
| Methacrylate | 5 | 5 | 1.0 |
| Acetate | 5 | 5 | 1.0 |
| Hydroxyl (O-H) | 3 | 3 | 1.0 |
| C-O single bond | 2 | 2 | 1.0 |
| Triglyceride | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 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 |
|---|---|---|---|
| PMMA | 2951, 1722, 1383 | Methacrylate, Alkyl C-H, Methoxy (OCH3) | 1 |
| PVP | 2951, 2983, 1648 | Alkyl C-H, Methacrylate | 1 |
| SiO2 | 2951, 1739, 699 | Alkyl C-H, Methoxy (OCH3) | 1 |
| sodium alginate | 2951, 1636, 1080 | Alkyl C-H, Methacrylate, Methoxy (OCH3) | 1 |
| PVC | 2951, 834, 1195 | Alkyl C-H, Methoxy (OCH3), Methacrylate | 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 2951 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
-
Acetate confidence 1.0
“cm-1 30 wt% NH 4Cl) PBEs at hydroxyl band region Similarly, vibrational band of C-H at 2927 cm-1 cm-1 between 3600 and 2800 and C-O band region and 2951 are due to Cornstarch and PVP, cm-1 cm-1 between 1080 and 960 is shown in Fig.”
Investigations of biodegradable polymer blend electrolytes based on Cornstarch: PVP: NH4Cl and its potential application in solid-state batteries DOI: 10.1007/s10854-021-05266-1 -
Alkyl C-H confidence 1.0
“ging mode at The peaks at 2951, 1721, 1449 and 1159cm-1 are assigned to CH stretching, C O stretching, CH 3 stretching and O CH stretching vibrations, respectively, in 3 Fig.5.”
Ramesh 等 - 2007 - FTIR studies of PVCPMMA blend based polymer elect DOI: 10.1016/j.saa.2006.06.012 -
Alkyl C-H confidence 1.0
“1st peak (3285.35 cm-1) belongs to (CH=CH 2) group of allyl, 2nd peak (2950.9 cm-1) belongs to group of aliphatic CH, 3rd peak (1638.15 cm-1) belongs to C=C, 4th peak (1032 cm-1) belongs to S=O, 6th peak (891.88 cm-1) belongs to C-S, and 7t”
Tasci 等 - 2016 - Determination of alliin and allicin in the plant o DOI: 10.17660/ActaHortic.2016.1143.19 -
Alkyl C-H confidence 1.0
“The characteristic peaks at 2951 cm-1 present the C-H stretching of the alkane groups, while the peak band at 935 cm-1 represents the C-O stretching vibration.”
Bhatia 等 - 2023 - The Effect of Sage (Salvia sclarea) Essential Oil DOI: 10.3390/gels9030233 -
Hydroxyl (O-H) confidence 1.0
“The use cm-1 cm- (O-C-C stretching), 3556 (O-H stretching), 2951 of some polymers also allows, at least in principle, to 1 (asymmetric stretching of methylene group) and 1454 achieve controlled release and the sustained drug levels cm-1 (O-”
Chouhan 和 Bajpai - 2009 - Real time in vitro studies of doxorubicin release DOI: 10.1186/1477-3155-7-5 -
Hydroxyl (O-H) confidence 1.0
“SIM is cm-1 is characterized by distinctive bands at wavenumbers of 3547 (free O-H stretchcharacterized by distinctive bands at wavenumbers of 3547 cm-1 (free O-H stretching vicm-1, cm-1, cm-1, cm-1 ing vibration), 2951 2930 2872 1467 (alip”
Preformulation Studies of Ezetimibe-Simvastatin Solid Dispersions in the Development of Fixed-Dose Combinations DOI: 10.3390/pharmaceutics14050912 -
Alkyl C-H confidence 1.0
“LLM confirmed rule peak-group candidate”
Screening of Fenofibrate-Simvastatin Solid Dispersions in the Development of Fixed-Dose Formulations for the Treatment of Lipid Disorders DOI: 10.3390/pharmaceutics15020603 -
Alkyl C-H confidence 1.0
“The bands with the maxima at 2951 and 2852 correspond to the stretching vibrations of -C-H in -CH 3, CH 2, present in the aliphatic groups in triglycerides.”
Comparative Analysis of Phytochemicals and Antioxidant Properties of Borage Oil (Borago officinalis L.) and Milk Thistle (Silybum marianum Gaertn) DOI: 10.3390/app13042560
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