What absorbs at 940 cm⁻¹ in an FTIR spectrum?
A band near 940 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 940 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 |
|---|---|---|---|
| Silicon-oxygen (Si-O) | 10 | 7 | 1.0 |
| Silicon (Si) | 8 | 6 | 1.0 |
| Methacrylate | 5 | 5 | 1.0 |
| C-O single bond | 4 | 4 | 1.0 |
| Acetate | 4 | 4 | 1.0 |
| Hydroxyl (O-H) | 4 | 4 | 1.0 |
| Methoxy (OCH3) | 3 | 3 | 1.0 |
| C c single bond | 3 | 3 | 1.0 |
| Ester | 3 | 3 | 1.0 |
| Silanol (Si-OH) | 3 | 3 | 1.0 |
| Hydrogen bond | 2 | 2 | 1.0 |
| Amide | 2 | 2 | 1.0 |
| N h | 2 | 2 | 1.0 |
| Carbonyl (C=O) | 2 | 2 | 1.0 |
| Borate | 2 | 2 | 1.0 |
| Silicon carbon | 2 | 1 | 1.0 |
| Siloxane (Si-O-Si) | 2 | 1 | 1.0 |
| Oxygen heterocycle | 2 | 1 | 1.0 |
| Metal oxygen | 1 | 1 | 1.0 |
| C=n | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Carboxyl (COOH) | 1 | 1 | 1.0 |
| Metal hydroxyl | 1 | 1 | 1.0 |
| C-S single bond | 1 | 1 | 1.0 |
| Alkyl C-H | 1 | 1 | 1.0 |
| Silicate | 1 | 1 | 1.0 |
| Phosphate (PO4) | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| Thiol | 1 | 0 | 1.0 |
| Boron nitrogen | 1 | 0 | 1.0 |
| Silicon fluorine | 1 | 0 | 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 |
|---|---|---|---|
| polymer | 940, 1718, 1722 | Methacrylate, C-O single bond | 1 |
| protein | 940, 1650, 1640 | Methacrylate | 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 940 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
-
Silicon (Si) confidence 1.0
“˜ (cid:110) IR band position at 940 against the isotopic substitution ˜ (cid:110) R 1 confirmed that this band belongs to silicon fluorides such as in terms of the measurable quantities.”
Han 和 Aydil - 1997 - Structure and chemical composition of fluorinated DOI: 10.1116/1.580845 -
Silicon (Si) confidence 1.0
“When annealed in nitrogen at different temperatures for varicm(cid:50)1 keeps almost unous durations, the peak at 807 cm(cid:50)1 changed, and the peak at 886 decreases gradually, cm(cid:50)1 cm(cid:50)1 peak at 940 is associated with the b”
Huang 和 Zhai - 1997 - Fourier transform infrared study of porous silicon DOI: 10.1116/1.589575 -
confidence 1.0
“There are 4 peaks arising from Si-O stretching vibrations in the region from 940 to cm21 1140 [16].”
Loo 和 Gleason - 2004 - Investigation of polymer and nanoclay orientation DOI: 10.1016/j.polymer.2004.06.025 -
C c single bond confidence 1.0
“5c highlight peaks 940 is also dominant in PC 2 in the glycated samples cm-1 cm-1 N-C-C at 1040 and therefore it could be vibrations from the formation and 1121 as contributing to the most var-”
Mcavan 等 - 2020 - Quantification of protein glycation using vibratio DOI: 10.1039/c9an02318f -
confidence 1.0
“After the 940cm¹1 sufficiently, mixture was stirred MMHy deuterated partially is the second harmonic mode of N at the As site N-H structure.27) was separated by strong base.”
Ohshita 等 - 2014 - N-H related defects in GaAsN grown through chemica DOI: 10.7567/JJAP.53.031001 -
Borate confidence 1.0
“components at 940 and 1058 All these bands are Density of states attributed to the stretching vibration in [BO 4] units [30].”
Rada 等 - 2009 - Structural and electronic properties of tellurite DOI: 10.1007/s10853-009-3433-8 -
Carbohydrate confidence 1.0
“vibrational peak at about 1160 the peak at a pyranose ring of cm(cid:0) 1, and the sulfate-based absorption peak at about about 940 Infrared spectroscopy was used to evaluate the structural changes in cm(cid:0) 1.”
Shan 等 - 2020 - Rheological and structural properties of ovomucin DOI: 10.1016/j.foodhyd.2019.105393 -
Silicon carbon confidence 1.0
“x phonon energy of any of the crystalline polytypes of SiC is (cid:4)see (cid:1)b(cid:2)(cid:5), a high resolution image plot which indicates that cm-1,33 (cid:3)940 cm-1 the Raman bands at can be ex972 T a=900 °C, the the as-deposited samp”
Song 等 - 2008 - Structural characterization of annealed Si1-xCxSi DOI: 10.1063/1.2909913
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.