What absorbs at 2928 cm⁻¹ in an FTIR spectrum?
A band near 2928 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 2928 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 | 61 | 57 | 1.0 |
| Hydroxyl (O-H) | 11 | 11 | 1.0 |
| Lipid | 4 | 3 | 1.0 |
| Aromatic ring | 4 | 3 | 1.0 |
| Methyl | 3 | 3 | 1.0 |
| Carboxyl (COOH) | 3 | 3 | 1.0 |
| Methacrylate | 3 | 3 | 1.0 |
| Acetate | 3 | 3 | 1.0 |
| Protein | 2 | 2 | 1.0 |
| Hydrogen bond | 2 | 2 | 1.0 |
| Methoxy (OCH3) | 2 | 2 | 1.0 |
| C-O single bond | 2 | 2 | 1.0 |
| Alkene (C=C) | 2 | 2 | 1.0 |
| Fatty acid | 2 | 1 | 1.0 |
| Silanol (Si-OH) | 1 | 1 | 1.0 |
| N h | 1 | 1 | 1.0 |
| Chitosan | 1 | 1 | 1.0 |
| Ammonium | 1 | 1 | 1.0 |
| Thiol | 1 | 1 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| Amide | 1 | 1 | 1.0 |
| N-O bond | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| Oxygen heterocycle | 1 | 1 | 1.0 |
| Amine primary | 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 |
|---|---|---|---|
| zinc oxide | 2928, 1627, 1638 | Alkyl C-H | 1 |
| zinc oxide nanoparticles | 2928, 1744, 1627 | Alkyl C-H, Hydroxyl (O-H) | 1 |
| silver nanoparticles | 2928, 1636, 1631 | Hydroxyl (O-H), 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 2928 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
“The vibrations 2928 and 2848 are assigned to asymmetric stretching and 7 symmetric stretching respectively of the acyl -CH groups [24, 29, 30].”
Fourier transform infrared microspectroscopy detects biochemical changes during C. elegans lifespan DOI: 10.1016/j.vibspec.2019.04.005 -
Alkene (C=C) confidence 1.0
“2928 2851 1740 1468 724 Previous works [45] reported peaks cm-1 cm-1 in the region 3000 and 2928 corresponding to the stretching vibrations of C=CH.”
The Effect of High-Intensity Ultrasound and Natural Oils on the Extraction and Antioxidant Activity of Lycopene from Tomato (Solanum lycopersicum) Waste DOI: 10.3390/antiox11071404 -
Alkyl C-H confidence 1.0
“phenols and amide groups of proteins have been shown to cm-1 The bands at 2928 correspond to the C-H stretching act as capping agent which prevented agglomeration and vibrations which corresponds to alkane groups.”
Dhayalan 等 - 2021 - Eco friendly synthesis and characterization of zin DOI: 10.1515/nanofab-2020-0104 -
Alkyl C-H confidence 1.0
“The presence of cm-1 C-H stretching vibrations in the broad spectrum of the peak at 2928 suggests the presence of alkanes or”
Nematicidal activity of seaweed-synthesized silver nanoparticles and extracts against Meloidogyne incognita on tomato plants DOI: 10.1038/s41598-022-06600-1 -
Alkyl C-H confidence 1.0
“The peak at 2928 is assigned to 54 55 cm-1 C-H asymmetric stretching.”
Hassanien 等 - 2019 - Novel green route to synthesize cadmium oxide@grap DOI: 10.1088/2053-1591/ab23ac -
Lipid confidence 1.0
“Peaks at 2928 and had a higher intensity and were attributed to lipids CH and CH 2 3 C�O stretching vibrationand of the carbonylgroups belonging tothe triacylglycerols, respectively.”
Hssaini 等 - 2022 - Do Pollination and Pollen Sources Affect Fig Seed DOI: 10.1155/2022/3969165 -
Alkyl C-H confidence 1.0
“cm-1 In addition, a new peak emerges at 2928 which can be assigned to C-H (bond with NH 2) as can be seen in spectrum b (s-TEMPO-NC).”
Indarti 等 - 2019 - Silylation of TEMPO oxidized nanocellulose from oi DOI: 10.1016/j.ijbiomac.2019.05.161 -
Alkyl C-H confidence 1.0
“cm-1 741 (ring vibration due to 1,2-disubstituted benzene) cm-1 756 cm-1 2-HP-(cid:2)-CD, 3401 ( OH stretching) cm-1 2928 ( CH stretching) cm-1 (H O H bending) 1652 cm-1 (C H stretching) 1164”
Telmisartan complex augments solubility, dissolution and drug delivery in prostate cancer cells DOI: 10.1016/j.carbpol.2013.09.077
Have a spectrum with this band?
Upload your FTIR spectrum and get a full interpretation report — peak assignments with literature citations, library matches, and a literature-backed analysis — in seconds.