What absorbs at 843 cm⁻¹ in an FTIR spectrum?
A band near 843 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 843 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 | 4 | 3 | 1.0 |
| Methoxy (OCH3) | 2 | 2 | 1.0 |
| Methacrylate | 2 | 2 | 1.0 |
| Acetate | 2 | 2 | 1.0 |
| C-O single bond | 2 | 2 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| Methyl | 1 | 1 | 1.0 |
| Silicon carbon | 1 | 1 | 1.0 |
| Silicon (Si) | 1 | 1 | 1.0 |
| Sulfate (SO4) | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| Oxygen heterocycle | 1 | 1 | 0.9 |
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 |
|---|---|---|---|
| Polypropylene | 843, 1030, 1600 | Alkyl C-H, Methacrylate, Acetate | 1 |
| glycerol | 843, 1585, 1630 | Methacrylate, Acetate, Alkyl C-H | 1 |
| carrageenan | 843, 1156, 1100 | Methacrylate, Acetate, Methoxy (OCH3) | 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 843 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
-
Secondary amine confidence 1.0
“at 500-700 vibration of a dye band S-O and S=O at 1022 and 1250 In addition, the bands at cm-1 cm-1 843 and 831 are derived from the vibration of the primary and secondary amine groups of the dye”
Studies of the potential of a native natural biosorbent for the elimination of an anionic textile dye Cibacron Blue in aqueous solution DOI: 10.1038/s41598-021-88657-y -
Alkyl C-H confidence 1.0
“After completely washing sponds to the C-O in PMMA structure while bending with distilled water, ethanol, absolute ethanol to remove vibrations of C-H exhibited absorption at 843, 914, and 986 hydrazine, sodium, and chlorine ion, the sample”
Hussain 等 - 2017 - Surfactant Incorporated Co Nanoparticles Polymer C DOI: 10.1155/2017/7191590 -
Acetate confidence 1.0
“cm-1): ν, FTIR (KBr, 3038 (=C-H stretch of the aromatic rings), 2933-2851 (C-H stretch of aliphatic chains), 1627 (-N=CHstretch), 1601, 1587, 1511 (C-C ring stretch), 1243, 1H-NMR 1163 (C-O-Cstretch), 843 (absorption band assigned to 1,4-ph”
Mesomorphic Behavior of Symmetric Azomethine Dimers Containing Different Chromophore Groups DOI: 10.3390/molecules26082183 -
C-O single bond confidence 1.0
“Sulfate-associated vibrations of carrageegroups in carrageenan can be found in the region from 900 to 1200 namely, at cm-1 cm-1 920 (C-O stretching in 3,6-anhydro-D-galactose), 1035 and 1063 (C-O and (D-galactose-4-sulphate), 1225 nan can a”
Edible Films from Carrageenan/Orange Essential Oil/Trehalose—Structure, Optical Properties, and Antimicrobial Activity DOI: 10.3390/polym13030332 -
Silicon (Si) confidence 1.0
“Si-CH3 group vibrations were assigned to the absorbance signals at 865 cm-1 and 843 cm-1.”
A Process Analytical Concept for In-Line FTIR Monitoring of Polysiloxane Formation DOI: 10.3390/polym12112473 -
Water (H2O) confidence 1.0
“The presence of cm-1, coordinated water was confirmed by the medium strength bands at 843 characteristic of rocking H 2O ( H 2O) frequencies [31,32].”
Zangaro 等 - 2019 - Study of the thermal behavior in oxidative and pyr DOI: 10.1016/j.jorganchem.2005.11.058. -
Oxygen heterocycle confidence 0.9
“Text states oxirane peaks (doublet) at 825 and 843 cm-1.”
Derahman 等 - 2019 - EPOXIDATION OF JATROPHA METHYL ESTERS VIA ACIDIC I DOI: 10.1590/0104-6632.20190362s20180326 -
Alkyl C-H confidence 0.9
“Explicit assignment in text.”
Glass Powder Additive on Recycled Polypropylene Filaments: A Sustainable Material in 3D Printing DOI: 10.3390/polym14010005
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