What absorbs at 1679 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 1679 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.

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 1679 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

• Carbonyl (C=O) confidence 1.0

  “2 shows that the dominant factors FTIR, which aside from showing bands typical of chitosan, influencing conductivity are the input amounts of TPAI and there is now a strong presence of new carbonyl bands at 1679 DMSO into the GPE system.”

  Conductivity or rheology? Tradeoff for competing properties in the fabrication of a gel polymer electrolyte based on chitosan-barbiturate derivative DOI: 10.1007/s11581-018-2515-5
• Acetate confidence 1.0

  “Free DMF molecules give rise to several bands, among them at 1679 at 1679 cm-1 (C=O stretching) and 1095 cm-1 (H3C-N stretching).”

  Butova 等 - 2023 - In Situ FTIR Spectroscopy for Scanning Accessible DOI: 10.3390/nano13101675
• Protein beta sheet confidence 1.0

  “In calculations of the relative content of different secondary structures an average of the cm-1, β-sheet two bands at 1679 and 1630 assigned to keratins with a secondary structure, was used”

  Greve 等 - 2008 - ATR-FTIR, FT-NIR and near-FT-Raman spectroscopic s DOI: 10.3233/SPE-2008-0365
• Hydrogen bond confidence 1.0

  “NIF-NIF intermolecular hydrogen bonding is further indicated by the cm-1 cm-1 presence of strong stretching vibrations at 1679 and 1689 that are also sensitive to intermolecular interactions (Cilurzo et al.”

  Physical properties and solubility studies of Nifedipine-PEG 1450/HPMCAS-HF solid dispersions DOI: 10.1039/C5PY01136A
• N-O bond confidence 1.0

  “No significant differences between groups were found for the areas of peaks 1655 cm-1 and 1679 cm-1.”

  Effects of Cannabis Use on the Protein and Lipid Profile of Olfactory Neuroepithelium Cells from Schizophrenia Patients Studied by Synchrotron-Based FTIR Spectroscopy DOI: 10.3390/biom10020329
• Protein alpha helix confidence 1.0

  “View Article Online Paper Nanoscale cm-1 α-helix, preferential, anisotropic behavior and the discovery of the characteristic of the peak of around 1679 is cm-1 effect β-sheet, β-turn keratin polarization (see Fig.”

  Stanic 等 - 2018 - The chemical fingerprint of hair melanosomes by in DOI: 10.1039/c8nr03146k
• Protein beta sheet confidence 1.0

  “(cm-1) amide I (C=O stretching, C-N stretching, β-sheet 1693 CNN deformation) of protein secondary structures [33,34] amide I (C=O stretching, C-N stretching, β-sheet 1679 CNN deformation) of protein”

  Application of FTIR Spectroscopy to Detect Changes in Skeletal Muscle Composition Due to Obesity with Insulin Resistance and STZ-Induced Diabetes DOI: 10.3390/ijms232012498