What absorbs at 2945 cm⁻¹ in an FTIR spectrum?
A band near 2945 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 2945 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 | 18 | 16 | 1.0 |
| Methacrylate | 6 | 6 | 1.0 |
| Acetate | 6 | 6 | 1.0 |
| Methyl | 5 | 5 | 1.0 |
| Methoxy (OCH3) | 5 | 5 | 1.0 |
| Amide | 4 | 4 | 1.0 |
| C-O single bond | 2 | 2 | 1.0 |
| Carbonyl (C=O) | 2 | 2 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| Silicon (Si) | 1 | 1 | 1.0 |
| Siloxane (Si-O-Si) | 1 | 1 | 1.0 |
| Silicon-oxygen (Si-O) | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Carboxyl (COOH) | 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 | 2945, 1100, 1080 | Alkyl C-H, Methacrylate, Acetate | 1 |
| polycaprolactone | 2945, 1580, 1751 | Methacrylate, Acetate, 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 2945 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
-
Amide confidence 1.0
“puted from 2945 to ) and the integrated area of hydrogenbondingconfigurationscanplayaroleindetermin2961cm-1 2945cm-1 asCH3 ing the line shape of amide A vibration [28-30].”
Calabro 等 - 2013 - 50 Hz Electromagnetic Field Produced Changes in FT DOI: 10.1155/2013/414393 -
Amide confidence 1.0
“1545cm-1 sorbance between 2945 and The asymmetric stretch peak Amide II: area under the peak: the Amide II peak is not 2920cm-1 affected at by water and can therefore be used to normalise the Amide has been related to lipid mobility and lip”
Interpersonal differences in the friction response of skin relate to FTIR measures for skin lipids and hydration DOI: 10.1016/j.colsurfb.2020.110883 -
Acetate confidence 1.0
“1, including the subtraction spectrum of presence of positive bands confirmed that the C-H normal tissue minus that of malignant tissue and speccm-1 and the C=O stretching vibrations at ~2945 trum of the malignant tissue minus that of norma”
Distinguishing malignant from normal stomach tissues and its <Emphasis Type="Italic">in vivo, in situ </Emphasis> measurement in operating process using FTIR Fiber-Optic techniques DOI: 10.1360/04yb0135 -
Alkyl C-H confidence 1.0
“The hTol provides IR bands due to cm-1, benzene ring C-H stretch modes in 3100-3000 while its methyl group shows two cm-1 bands due to antisymmetric stretch modes at about 2945 and 2920 and a band due to cm-1.”
Balacescu 等 - 2021 - Light Scattering and Absorption Complementarities DOI: 10.3390/app11115135 -
Alkyl C-H confidence 1.0
“cm-1, t Aromatic ring C=C-C stretching vibrations located at 1594 aliphatic C-H cm-1, stretching vibrations arises at 2945 and C-H bending vibration appears at 1444 and cm-1.5,39,40 cm-1 1375 The FTIR spectra of ADP showed C=O stretching vi”
Polymer-Assisted Aripiprazole-Adipic Acid Cocrystals Produced by Hot Melt Extrusion Techniques DOI: 10.1021/acs.cgd.0c00020. -
Alkyl C-H confidence 1.0
“LLM confirmed rule peak-group candidate”
Antibacterial and Cytotoxic Silica-Polycaprolactone- Chlorogenic Acid Hybrids by Sol–Gel Route DOI: 10.3390/molecules28083486 -
Alkyl C-H confidence 1.0
“800 and 850 these bands are located at 2945 and 2879 Surprisingly, these C-H stretching modes exactly correspond to C-H signatures of DND voluntary hydrogenated either by annealing or plasma treatments under H 2, as reported in literature [”
New Insights into the Reactivity of Detonation Nanodiamonds during the First Stages of Graphitization DOI: 10.3390/nano11102671 -
Amide confidence 1.0
“FTIR bands at 2945 and 2889 cm-1) peptide bond bands (amide I ~1640 and amide II ~1540 were not detected, suggesting that proteins are not related to mineral synthesis or their stabilization.”
Fragoso 等 - 2010 - Characterization of the CaCO3 biomineral in corall DOI: 10.7773/cm.v36i1.1606
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.