What absorbs at 2938 cm⁻¹ in an FTIR spectrum?
A band near 2938 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 2938 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 | 16 | 15 | 1.0 |
| N h | 3 | 3 | 1.0 |
| Hydroxyl (O-H) | 3 | 3 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| Methoxy (OCH3) | 1 | 1 | 1.0 |
| Methacrylate | 1 | 1 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| Acetate | 1 | 1 | 1.0 |
| Amide | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| C=n | 1 | 1 | 1.0 |
| Protein | 1 | 1 | 1.0 |
| Lignin | 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 |
|---|---|---|---|
| Silica | 2938, 1100, 1080 | Hydroxyl (O-H), Alkyl C-H | 1 |
| silica nanoparticles | 2938, 1718, 2925 | N h, Alkyl C-H, Hydroxyl (O-H) | 1 |
| rGO | 2938, 2358, 2930 | Hydroxyl (O-H), Alkyl C-H, N h | 1 |
| hydrogels | 2938, 3281, 1700 | Alkyl C-H, N h | 1 |
| lignin | 2938, 1035, 1510 | 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 2938 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
-
Lignin confidence 1.0
“While, combination 21 is rich in S/G type lignin as cm-1 to produce mediators such as N-heterocyclic and aromatic comfrom its high intensity S type lignin peaks at 2938 observed”
A strategic laccase mediated lignin degradation of lignocellulosic feedstocks for ethanol production DOI: 10.1016/j.indcrop.2016.08.009 -
Alkyl C-H confidence 1.0
“The peaks OH-stretching contribution in the region between ~3700 and ~3000 The cm-1 cm-1 at ~2979 cm-1 and ~2938 cm-1 are assigned to C-H stretching, while the peak centered at peaks at ~2979 and ~2938 are assigned to C-H stretching, while”
Hydrating Capabilities of the Biopolymers Produced by the Marine Thermophilic Bacillus horneckiae SBP3 as Evaluated by ATR-FTIR Spectroscopy DOI: 10.3390/ma15175988 -
Alkyl C-H confidence 1.0
“The cm-1 band at 2938 corresponds to CH asymmetric stretching T = 60 °C”
Devi 等 - 2019 - Structural and optical studies on PVA capped SnS f DOI: 10.1088/1674-4926/40/5/052101 -
Alkyl C-H confidence 1.0
“The FTIR spectrum for GW3 exhibited D, r, S, t where and represent the diffusion coefficient, radius, sp3 cm-1 absorption peaks for C-H stretch at 2938 and C=C”
Owonubi 等 - 2018 - Characterization and in vitro release kinetics of DOI: 10.1007/s40090-018-0139-2 -
Alkyl C-H confidence 1.0
“LLM confirmed rule peak-group candidate”
Ryu 等 - 2013 - Modification of Silica Nanoparticles with Bis[3-(t DOI: 10.7317/pk.2013.37.3.308 -
Alkyl C-H confidence 1.0
“LLM confirmed rule peak-group candidate”
Biocompatible and biodegradable elastomer/fibrinogen composite electrospun scaffolds for cardiac tissue regeneration DOI: 10.1039/c5ra20322h -
confidence 1.0
“In the same figures, band at cm-1 2938 corresponds to N-H stretching due to the addition of whey protein concentrate cm-1 as carrier, whereas the broad band at 3409 was due to the hydroxyl (O-H) stretching vibration.”
Development and Characterization of a Nutritionally Rich Spray-Dried Honey Powder DOI: 10.3390/foods10010162 -
C=n confidence 1.0
“In about the imiFT-IR spectrum of the Amp@SCMNPs can be observed the cm(cid:3)1), cm(cid:3)1) cm(cid:3)1 C-H ne@SCMNPs, the peak at 1636 peaks for (2938 and NH (3250, and 3427 is assigned to the 2 TGA curves of (a) SCMNPs, (b) GAA/imine@SCM”
Mo@GAA-Fe3O4 MNPs: a highly efficient and environmentally friendly heterogeneous magnetic nanocatalyst for the synthesis of polyhydroquinoline derivatives DOI: 10.1039/d1ra00396h
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.