What absorbs at 2975 cm⁻¹ in an FTIR spectrum?
A band near 2975 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 2975 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 | 13 | 13 | 1.0 |
| Methoxy (OCH3) | 3 | 3 | 1.0 |
| Methacrylate | 3 | 3 | 1.0 |
| Acetate | 3 | 3 | 1.0 |
| Methyl | 3 | 2 | 1.0 |
| Silicon carbon | 2 | 2 | 1.0 |
| Aromatic ring | 2 | 2 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Silicon (Si) | 1 | 1 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| N h | 1 | 1 | 0.8 |
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 |
|---|---|---|---|
| ZnO | 2975, 1400, 3430 | Alkyl C-H, Acetate, Methacrylate | 1 |
| lignin | 2975, 1035, 1510 | Alkyl C-H, Methacrylate, Acetate | 1 |
| PVP | 2975, 2983, 1648 | 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 2975 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 adsorption band at 2974.75 with the intensity ratios of CH2 asymmetric and symmetric stretching cm(cid:0) 1 bands at 2494.58 could indicate the occurrence of long-chain hydrocarbon derivatives, such as lipids and acid esters/- of CH3”
Biologically-induced synthetic manganese carbonate precipitate (BISMCP) for potential applications in heavy metal removal DOI: 10.1016/j.heliyon.2023.e15919 -
Alkyl C-H confidence 1.0
“The peak at 2975 is attributed to the 3 cm-1 stretching vibration absorption peak of the hydrocarbon [31].”
Liang 等 - 2020 - Thermal Kinetics of a Lignin-Based Flame Retardant DOI: 10.3390/polym12092123 -
Alkyl C-H confidence 1.0
“The band appeared at 2975 and 2895 is assigned to the CH asymmetrical stretching vibrations, confirm organic groups of PVP [13].”
Pandiyarajan 和 Karthikeyan - 2013 - Structural, thermal and optical properties of PVP DOI: 10.4028/www.scientific.net/AMR.678.253 -
Acetate confidence 1.0
“The symmetrical C-H stretching frequency of the -CH2and -CH3 groups in the 1132.15 1232.57 91 ethyl and the -CH2groups in the hydroxyethyl becomes intense at 2869, 2934 and 2975 cm-1.”
Aktas 等 - 2020 - A Novel Ag-N-Heterocyclic Carbene Complex Bearing DOI: 10.3390/cryst10030171 -
Alkyl C-H confidence 1.0
“- 1 - - The red and blue marks indicate how ethanol/water ratios affect the intensities of C H stretching (2975 cm ) and C H bending”
Assessment of quality of commercial hand sanitizers using Fourier transform infrared spectroscopy and gas chromatography DOI: 10.1016/j.mex.2023.102274 -
Alkyl C-H confidence 1.0
“1375 Alkane C-H stretching 2975 3000 3000 2833;”
Cerit 等 - 2016 - Effect of Modification with Various Epoxide Compou DOI: 10.1155/2016/4968365 -
Aromatic ring confidence 1.0
“LLM confirmed rule peak-group candidate”
Drais 和 Hussein - 2022 - Lipid-Polymer Hybrid Nanocarriers for Oral Deliver DOI: 10.34172/apb.2022.081 -
Alkyl C-H confidence 1.0
“cm-1 The peaks found in the 2975-2855 spectral region are associated with the C-H stretching vibrations of the aliphatic groups, and are present in the mean spectra of the stimulants, as well as in the spectra of hallucinogens.”
Principal Component Analysis Coupled with Artificial Neural Networks—A Combined Technique Classifying Small Molecular Structures Using a Concatenated Spectral Database DOI: 10.3390/ijms12106668
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