What absorbs at 2933 cm⁻¹ in an FTIR spectrum?
A band near 2933 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 2933 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 | 29 | 28 | 1.0 |
| Hydroxyl (O-H) | 5 | 5 | 1.0 |
| Methacrylate | 4 | 4 | 1.0 |
| Acetate | 4 | 4 | 1.0 |
| Methoxy (OCH3) | 3 | 3 | 1.0 |
| C-O single bond | 2 | 2 | 1.0 |
| Hydrogen bond | 2 | 2 | 1.0 |
| Methyl | 2 | 2 | 1.0 |
| Carboxyl (COOH) | 2 | 2 | 1.0 |
| Ring structure | 2 | 1 | 1.0 |
| N h | 1 | 1 | 1.0 |
| Lignin | 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 |
| Aromatic ring | 1 | 1 | 1.0 |
| Alkene (C=C) | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| N-O bond | 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 |
|---|---|---|---|
| pectin | 2933, 1746, 1150 | Methacrylate, Acetate, Alkyl C-H | 1 |
| lignin | 2933, 1035, 1510 | Alkyl C-H, Methacrylate, Acetate | 1 |
| gold nanoparticles | 2933, 1638, 3252 | Alkyl C-H, Methacrylate, Acetate | 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 2933 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
“(C=C bending and stretching mode), 1535 stretching A known amount of furan was injected into a conical mode), 1590, 1607, 1635 (vibrational mode of furan flaskcontaininga weighedquantity of MMTandfitted (C=O monomer), 1750 stretching mode),”
Preparation and evaluation of nanocomposites of polyfuran with Al2O3 and montmorillonite clay DOI: 10.1002/pi.1562 -
Alkyl C-H confidence 1.0
“cm-1 ∼2933 The peak observed at can be attributed to the CH 2 values of R and J in the cathodic compartment (Table 2) The”
Cristian 等 - 2015 - Removal of zinc ions from model wastewater system DOI: 10.1016/j.jwpe.2015.08.001 -
Alkyl C-H confidence 1.0
“The bands observed at 2933 and 2863 are respectively related to the C-H vibrationsandtheC-Hstretchinginmethoxygroups.Thebandat1708cm(cid:2)1isassignedto unconjugated C¼O stretching.”
Synthesis and characterization of lignin–melamine–formaldehyde resin DOI: 10.1177/0892705716632856 -
Alkyl C-H confidence 1.0
“So the higher surface cm-1, a strong C-H peak at 2933 peak around 3350 area of MMA grafted lignin is due to the combined”
Jacob 等 - 2013 - Green Synthesis for Lignin Plasticization Aqueous DOI: 10.7569/JRM.2012.634107 -
Alkyl C-H confidence 1.0
“FUNCTIONAL GROUPS cm-1 10 10 3364.31 NH strectching aliphatic amine NH strectching aliphatic amine cm-1 2933 CH stretching alkane”
Leemarose 等 - 2021 - Sustainable Synthesis of Gold Nanoparticles and it DOI: 10.13005/ojc/370216 -
Alkyl C-H confidence 1.0
“Differential scanning calorimetry (DSC) cm-1 2933 were credited to stretching of C-H bonds, these involved the CH, CH and CH stretching and bending vibraThermal stability of YAP incorporated pectin films was deter2 3 tions (Lorevice et al.,”
Nisar 等 - 2019 - Citrus pectin films enriched with thinned young ap DOI: 10.1080/19476337.2019.1640798 -
Hydroxyl (O-H) confidence 1.0
“The FT-IR analysis of the extract revealed 2932.96cm-1 different characteristic absorption peak values for various functional groups: (-OH stretch), (C-H 1588.91cm-1 (C (cid:30)N stretch), among others.”
Rotich 等 - 2022 - FT-IR Analysis of Beta vulgaris Peels and Pomace D DOI: 10.1155/2022/2233414 -
Alkyl C-H confidence 1.0
“cm-1 The band at 2933 donates the C-H asymmetric stretching of alkanes [72].”
Biosynthesis of Novel Tellurium Nanorods by Gayadomonas sp. TNPM15 Isolated from Mangrove Sediments and Assessment of Their Impact on Spore Germination and Ultrastructure of Phytopathogenic Fungi DOI: 10.3390/microorganisms11030558
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.