What absorbs at 781 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 781 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 authoritative rule. Always confirm against your sample context.

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 781 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

  “The cm-1 cm-1 absorption band at 781 and 1050 are assigned to the v 1symmetric vibration and v 3asymmetrical stretching vibration of the Si-O bond.”

  Ilmi 等 - 2020 - Multi-analytical characterizations of prehistoric DOI: 10.1016/j.microc.2020.104738
• confidence 1.0

  “cm-1, The spectra produced strong peaks at 521.38 and 516.39 corresponding to the C-I (stretching) functional group of alkyl halides, for the leaf and stem, respectively, as well as cm-1 a strong peak corresponding to the C-Cl (stretching)”

  Phytochemical Composition of Combretum molle (R. Br. ex G. Don.) Engl. & Diels Leaf and Stem Extracts DOI: 10.3390/plants12081702
• Alkyl C-H confidence 1.0

  “Both samples treated with TEMPO derivatives show the characteristic signals of their functional groups: in particular, the band at 1709 and 1717 cm-1 can be associated with the cm-1 functional groups: in particular, the band at 1709 and 171”

  Cicogna 等 - 2022 - Surface Functionalization of Face Masks with Cold DOI: 10.3390/molecules27238632
• Oxalate confidence 1.0

  “The FTIR spectrum peaks at 780.7, 1336.4, and 1631.0 all correspond to reported peak positions for sodium oxalate [16].”

  Evaluation of Formate Salt PCM’s for Latent Heat Thermal Energy Storage DOI: 10.3390/en14030765
• confidence 1.0

  “The vibrational band centred at 781 cm-1 is ascribed to the stretching mode modes due to the formation of nonbridge oxygen.”

  Effect of Yb3+ on the Structural and Visible to Near-Infrared Wavelength Photoluminescence Properties in Sm3+-Yb3+-Codoped Barium Fluorotellurite Glasses DOI: 10.3390/ma15093314
• C c single bond confidence 1.0

  “Furthermore, for the spectrum of cm-1 1545, and 1552 cm-1, respectively, can be attributed to the C-C stretching vibration of benzene ring HACSa, HACCa, HACPc, and HACGa, absorption peaks at 781, 767, 772, 735, 739 corresponded 1478cm-1 [3,”

  Modification of Hydroxypropyltrimethyl Ammonium Chitosan with Organic Acid: Synthesis, Characterization, and Antioxidant Activity DOI: 10.3390/polym12112460
• Silicon (Si) confidence 1.0

  “The peaks at 113 cm-1 cm-1 876 cm-1 and 781 cm-1 were assigned to Si-O-Si symmetric stretching vibrations [36].”

  Adsorption of Hexavalent Chromium Using Banana Pseudostem Biochar and Its Mechanism DOI: 10.3390/su10114250
• Nucleic acid confidence 1.0

  “LLM confirmed rule peak-group candidate”

  Zelig 等 - 2010 - Biochemical analysis and quantification of hematop DOI: 10.1117/1.3442728(cid:4)