What absorbs at 842 cm⁻¹ in an FTIR spectrum?
A band near 842 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 842 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 | 5 | 4 | 1.0 |
| Silicon (Si) | 4 | 4 | 1.0 |
| Silicon-oxygen (Si-O) | 4 | 4 | 1.0 |
| Siloxane (Si-O-Si) | 3 | 3 | 1.0 |
| Methoxy (OCH3) | 2 | 2 | 1.0 |
| Methacrylate | 2 | 2 | 1.0 |
| Acetate | 2 | 2 | 1.0 |
| Methyl | 2 | 2 | 1.0 |
| C c single bond | 2 | 2 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Amide | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Chitosan | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Alkene (C=C) | 1 | 1 | 1.0 |
| Metal oxygen | 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 |
|---|---|---|---|
| silica | 842, 1100, 1080 | Silicon-oxygen (Si-O), Silicon (Si), Siloxane (Si-O-Si) | 2 |
| PVA | 842, 1660, 2930 | Alkyl C-H | 1 |
| PEG | 842, 1650, 1342 | Alkyl C-H | 1 |
| MWCNT | 842, 2876, 1430 | Alkyl C-H | 1 |
| Polyurethane | 842, 2270, 1700 | Alkyl C-H | 1 |
| nanocomposites | 842, 1717, 1630 | 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 842 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
“To assess the 1st, 2nd 9th biodeterioration of the TDR media, ATR was performed for the raw, and week TDR cm-1 media samples and in the raw TDR, two important bands, 842 and 2962 were noticed representing -CH=CH and -CH 3.”
Yadav 等 - 2021 - Evaluation of tire derived rubber (TDR) fixed biof DOI: 10.1080/09593330.2020.1737736 -
Ring structure confidence 1.0
“The presence ring.72 cm-1 imidazole In the spectrum of ([DEIm][PF 6]) (Figure of the [PF 6] anion was indicated by a sharp peak at 842 3787”
Ionic Liquid Functionalized Metal–Organic Framework ([DEIm][PF6]@MOF-5): Synthesis, Characterization, and Catalytic Application in the Reduction of 4-Nitrophenol DOI: 10.1021/acsomega.2c05808 -
Alkyl C-H confidence 1.0
“LLM confirmed rule peak-group candidate”
Aziz 等 - 2019 - Structural and Optical Characteristics of PVAC-Do DOI: 10.3390/nano9020216 -
C c single bond confidence 1.0
“The peak corresponding to C-O stretching occurs at approximately 1089 while at approximately 1089 cm-1 while the band at 842 cm-1 is attributed to the C-C stretching vibration [8,41].”
Preparation and Characterization of Polyvinyl Alcohol-Chitosan Composite Films Reinforced with Cellulose Nanofiber DOI: 10.3390/ma9080644 -
Silicon (Si) confidence 1.0
“The strong absorption bands appearing at 1047.74 cm-1 and 841.77 cm-1 are the characteristic peaks of the asymmetric and symmetric stretching vibration of Si-O-Si, respectively [33,36-38].”
Cimavilla-Roman 等 - 2020 - Influence of silica aerogel particles on the foami DOI: 10.1016/j.eurpolymj.2020.109884 -
Alkyl C-H confidence 1.0
“However an increase of the peaks at 842 and 756 attributed to methyl”
Effects of 400 keV electrons flux on two space grade silicone rubbers DOI: 10.1016/j.matchemphys.2013.05.002 -
Silicon (Si) confidence 1.0
“2315 cm-1 cm-1 Based on spectra analysis in Figure 2, PLLAat 960 and around 1100 corresponds to the FTIR cm-1 PEG/SiO membrane exhibited almost similar peaks with Si-O group while peak at 842 was attributed to 2 copolymer membrane in their”
Kamil 等 - 2020 - Treatment of Palm Oil Mill Effluent by Poly(L-Lact DOI: 10.17576/jsm-2020-4909-28 -
Alkyl C-H confidence 1.0
“From the FTIR spectra of pristine PEG, the charactershows minor characteristic bands at 3428, 1288, and 1250 which represent the O-H istic peaks at 2876, 1453, 956, and 842 cm-1 were assigned to the C-H stretching and bendstretching and ben”
Kumar 等 - 2022 - Flexible Temperature Sensor Utilizing MWCNT Doped DOI: 10.3390/mi13020197
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