What absorbs at 2929 cm⁻¹ in an FTIR spectrum?
A band near 2929 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 2929 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 | 50 | 48 | 1.0 |
| Hydroxyl (O-H) | 11 | 10 | 1.0 |
| Hydrogen bond | 4 | 4 | 1.0 |
| Methyl | 4 | 3 | 1.0 |
| N h | 3 | 3 | 1.0 |
| Lipid | 2 | 2 | 1.0 |
| Thiol | 2 | 2 | 1.0 |
| Carbonyl (C=O) | 2 | 1 | 1.0 |
| Carboxyl (COOH) | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| Alkene (C=C) | 1 | 1 | 1.0 |
| Silicon-oxygen (Si-O) | 1 | 1 | 1.0 |
| Silicon (Si) | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| Triglyceride | 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 |
| Ring structure | 1 | 1 | 1.0 |
| Secondary amine | 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 |
|---|---|---|---|
| copper oxide | 2929, 624, 1686 | 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 2929 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
“stretching sp3, C-H stretching O-H 2929 - - -”
Effect of Calcination Temperature on Structural, Morphological and Optical Properties of Copper Oxide Nanostructures Derived from Garcinia mangostana L. Leaf Extract DOI: 10.3390/nano12203589 -
Alkyl C-H confidence 1.0
“LLM confirmed rule peak-group candidate”
Cheng 等 - 2011 - The Research on the Longitudinal Tensile Strength DOI: 10.4028/www.scientific.net/AMR.183-185.2014 -
N h confidence 1.0
“cm(cid:1)1 vibration,28 assigned as NH stretching at 2929 and in bonyl stretching absorption at 1723 2 cm(cid:1)1”
Characterization of chemically modified wood fibers using FTIR spectroscopy for biocomposites DOI: 10.1002/app.31746 -
Alkyl C-H confidence 1.0
“A notable peak observed at 2929 cm-1 was considered to be due to C-H cm-1 the stretching vibrations of O-H and N-H groups.”
Kim 等 - 2022 - Removal of Methyl Red from Aqueous Solution Using DOI: 10.3390/ijerph19159030 -
Hydroxyl (O-H) confidence 1.0
“Figure.3 showed that the mid-strong 3451cm-1 peak at was the O-H stretching vibration absorption peak, the C-H stretching vibration cm-1,2959cm-1, 2929cm-1, 2879cm-1, 2746cm-1, absorption peaks were located at 3061 and the peaks 2247cm-1, 2”
Li 等 - 2011 - The detection of Cypermethrin on the surface of Ap DOI: 10.4028/www.scientific.net/AMR.287-290.2991 -
Ring structure confidence 1.0
“vibration;thesharpbandat2929cm(cid:1)1wasattributedtoCeHbond stretching associated with the ring methane hydrogen atoms;”
Modifications of structure and physicochemical properties of maize starch by γ-irradiation treatments DOI: 10.1016/j.lwt.2011.10.012 -
Alkyl C-H confidence 1.0
“O-H stretching 3444.2 3416.28 3424.96 3418.21 C-H asymmetric stretching 2929.3 2925.48 - 2927.41 2347.91 2348.87 2348.87 B-O stretching BO3 1375 1379.82 1369.21 1751.05”
ς(3) measurement and optical power limiting behavior of manganese doped lithium tetraborate nanoparticles DOI: 10.1016/j.saa.2014.09.116 -
Acetate confidence 1.0
“bond.30 cm-1 cm-1 vibration of the C-O The bands at 2929 and 3403 are characteristic of 233 vibration.31,32 the C-H and O-H stretching Compared with β-cyclodextrin, the OCD 234 cm-1, showed a new stretching vibration peak at 1724 which was”
Niu 等 - 2019 - Preparation and Characterization of a Modified-bet DOI: 10.1021/acs.jafc.9b05467
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