What absorbs at 2856 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 2856 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

Ranking reflects accumulated literature evidence, not a single fixed rule. Always confirm against your sample context.

Possible materials

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 2856 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 3030cm-1 (=C-H methylene protons at 5H of the 3-Octanoylthio-1-propyltriethoxysilane peak at stretching vibration) remains same after 2856cm-1 modification.”

  Reactive grafting of 3-octanoylthio-1-propyltriethoxysilane in styrene butadiene rubber_ Characterization and its effect on silica reinforced tire composites DOI: 10.1016/j.polymer.2019.121693
• Thiol confidence 1.0

  “The spectrometer was Fe3+ 2122 blanked with air at room temperature for the raw samples or with a 2550-2590 Cys S-H stretch 2856 Methylene C-H stretch clean piece of the white cotton T-shirt or white copier paper for 2920”

  Elkins - 2011 - Rapid Presumptive Fingerprinting of Body Fluids DOI: 10.1111/j.1556-4029.2011.01870.x
• Alkyl C-H confidence 1.0

  “The antisymmetric stretching vibration absorption band near 2924 belongs to the -CH group, 2 cm-1 and the symmetric stretching vibration absorption band near 2856 belongs to the -CH group, which mainly”

  Luan 等 - 2020 - Spectral characteristics on increasing hydrophilic DOI: 10.1016/j.saa.2020.118350
• Alkyl C-H confidence 1.0

  “cm-1, diffusion, C-H 24 h of followed by a single terminal ICP-MS PEG groups on the US-AuNP-PEG-DFO, at 2882 possibly overlaps the lipid symmetric CH stretching at 2856 measurement.”

  High-Sensitivity Permeation Analysis of Ultrasmall Nanoparticles Across the Skin by Positron Emission Tomography DOI: 10.1021/acs.bioconjchem.1c00017
• Aromatic ring confidence 1.0

  “of aromatic aldehydes and CO is indicated by the band at 2856 A protein-specific 2”

  Biosynthesis and Characterization of Silver Nanoparticles Using Tribulus terrestris Seeds: Revealed Promising Antidiabetic Potentials DOI: 10.3390/molecules28104203
• Alkyl C-H confidence 1.0

  “This result indicated that the low rank NM 0.012 Sum of fit peaks peak 2856 coal and high rank NX coal had shorter and more branched aliphatic peak 2924 0.010 chainsontheedgeofthearomaticnucleicomparedtothoseofmedium peak 2960 peak 2874”

  FTIR study on structural changes of different-rank coals caused by single/multiple extraction with cyclohexanone and NMP/CS2 mixed solvent DOI: 10.1016/j.fuproc.2016.08.035
• Triglyceride confidence 1.0

  “The sharp peaks at 2922 and 2856 are mainly due to the triglycerides comcm-1 The sharp peaks at 2922 and 2856 cm-1 are mainly due to the triglycerides comprising 83prising 83-86% of total neutral lipids in RBO.”

  The Influence of Emulsifiers on the Physiochemical Behavior of Soy Wax/Rice Bran Oil-Based Oleogels and Their Application in Nutraceutical Delivery DOI: 10.3390/gels9010047
• Alkyl C-H confidence 1.0

  “Related to the bidentate formate, the C-H stretching of the formate group at 2856 cm-1 is most intensive [36,41].”

  The Activity of Ultrafine Cu Clusters Encapsulated in Nano-Zeolite for Selective Hydrogenation of CO2 to Methanol DOI: 10.3390/catal12111296