What absorbs at 2934 cm⁻¹ in an FTIR spectrum?
A band near 2934 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 2934 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 | 24 | 21 | 1.0 |
| Hydroxyl (O-H) | 7 | 7 | 1.0 |
| Methyl | 4 | 4 | 1.0 |
| Methoxy (OCH3) | 3 | 3 | 1.0 |
| Methacrylate | 3 | 3 | 1.0 |
| Acetate | 3 | 3 | 1.0 |
| C-O single bond | 2 | 2 | 1.0 |
| Carbohydrate | 2 | 2 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Carboxyl (COOH) | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| Amide | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| N h | 1 | 1 | 1.0 |
| Lignin | 1 | 1 | 0.7 |
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 |
|---|---|---|---|
| Nanocellulose | 2934, 1540, 1646 | Alkyl C-H, Hydroxyl (O-H), Methoxy (OCH3) | 1 |
| microplastics | 2934, 1643, 1614 | Alkyl C-H, Hydroxyl (O-H) | 1 |
| PHB | 2934, 3440, 1724 | Alkyl C-H, Methoxy (OCH3), Methyl | 1 |
| ZnO | 2934, 1400, 3430 | Hydroxyl (O-H), 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 2934 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
“1 fied PHB showed signals of a chemical shift at δ 1.22band at 3436 cmThe bands at 2934 and 2976 cmwere = 1.34 ppm as a doublet of the methyl group, and a pair of assigned to C-H stretching methyl and methylene groups;”
Production and optimization of bioplastic (Polyhydroxybutyrate) from DOI: 10.1186/s12866-022-02593-z -
Alkyl C-H confidence 1.0
“The peaks at 2934 and cm-1 1380 were attributed to the stretching and bending of C-H bond.”
Hu 等 - 2021 - Properties and Structure of Modified Taro Starch DOI: 10.1002/star.202000252. -
Alkyl C-H confidence 1.0
“The band at in greater development and aggregation of the nucleation cm-1 2934 was due to C-H stretching vibrations and the crystallite.”
Bright red luminescence emission of macroporous honeycomb-like Eu3+ ion-doped ZnO nanoparticles developed by gel-combustion technique DOI: 10.1007/s42452-020-2639-x -
Hydroxyl (O-H) confidence 1.0
“In the gluten spectrum, CH, cm(cid:1)1 and NH or OH stretching modes presented peaks placed at 2934 and 3397 wavenumbers, respectively.”
Interactions between polyols and wheat biopolymers in a bread model system fortified with inulin: A Fourier transform infrared study DOI: 10.1016/j.heliyon.2018. -
N h confidence 1.0
“The Nylon 6 cm-1 spectrum shows a sharp and very strong band at 3296 that it is assigned to NH stretching, as well cm-1 as two bands located at 2934 and 2859 assigned to the asymmetric and symmetric stretching cm-1,”
Synthesis of Nylon 6/Modified Carbon Black Nanocomposites for Application in Uric Acid Adsorption DOI: 10.3390/ma13225173 -
Alkyl C-H confidence 1.0
“During the pyrolysis of PVC, the first reaction took place after HCl was removed by the cleavage of the C-Cl bond at 605 K, and then the pyrolysis products containing CH2 bending of 2934 cm-1 appeared in the second stage.”
Pyrolysis Process of Mixed Microplastics Using TG-FTIR and TED-GC-MS DOI: 10.3390/polym15010241 -
Alkyl C-H confidence 1.0
“cm-1 cm-1 cm-1 and from 2870 characteristic to C-H stretching of -CH group and 2934 and 2844 3 C-H bond in -CH are strong in K_AT, which suggest the occurrence of new chain-ends due to the”
Bacterial Nanocellulose from Side-Streams of Kombucha Beverages Production: Preparation and Physical-Chemical Properties DOI: 10.3390/polym9080374 -
Alkyl C-H confidence 1.0
“LLM confirmed rule peak-group candidate”
Biodegradation of P(3HB-co-4HB) powder by Pseudomonas mendocina for preparation low-molecular-mass P(3HB-co-4HB) DOI: 10.1007/s13205-017-0824-4
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