What absorbs at 1689 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 1689 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 1689 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

  “Notably, the similar solvent, showed a similar spectral pattern cm-1 absorbance peaks around 1689, 1721 and 1740 qualitatively albeit different values of absorption denoted the absorption of the carbonyl functional group, intensity.”

  Aziz 等 - 2020 - FTIR and HPLC-Based Metabolomics of Yacon Leaves E DOI: 10.22146/ijc.43453
• Alkene (C=C) confidence 1.0

  “There are C-O peak at 998 2 cm-1 cm-1 and C=C peak at 1689 indicating the formation of rGO.Moreover, the composite also has”

  Nurdiansah 等 - 2020 - Synthesis of ZnOrGOTiO2 Composite and Its Photoc DOI: 10.1088/1757-899X/833/1/012028
• Protein beta sheet confidence 1.0

  “For the W60V mutant, although ported by the well-resolved spectral component at the IR response of the crystalline protein is similar to that cm(cid:4)1, b due to turn absorption (11), which is narrower 2m, the solution spectrum displays mi”

  Structure, Stability, and Aggregation of β-2 Microglobulin Mutants: Insights from a Fourier Transform Infrared Study in Solution and in the Crystalline State DOI: 10.1016/j.bpj.2012.02.045
• Metal oxygen confidence 1.0

  “With the incorporation of GO with PVA, the FTIR spectra indicated the formation of common properties such as O-H, C=O, C=C, -CH2, C-O stretching, and C-H bending at 3741.18 cm-1, 1774.84 cm-1, 1689.04 cm-1, 1511.76 cm-1, 1182.03 cm-1, and 8”

  Evaluation of Structural and Optical Properties of Graphene Oxide-Polyvinyl Alcohol Thin Film and Its Potential for Pesticide Detection Using an Optical Method DOI: 10.3390/photonics9050300
• Alkene (C=C) confidence 1.0

  “The formation of a new peak at around 1689 and 1575 cm-1, corresponding to the vibration modes of C=C bonds in the aromatic group, indicated the formation of graphite [26].”

  Hung Kim Nguyen 等 - 2020 - Preparation of a Novel Flame Retardant Formulation DOI: 10.3390/ma13010054
• Isocyanate confidence 1.0

  “Eventually, allophanates, obtained from the reaction(s) between urethane and isocyanate may also be present [28,29] with C O stretching vibration absorption bands at 1710 cm-1 [30] or at 1724 and 1689 cm-1 [31].”

  Chemical gradients in PIR foams as probed by ATR-FTIR analysis and consequences on fire resistance DOI: 10.1016/j.polymertesting.2020.106972
• Protein beta turn confidence 1.0

  “Band positions cm-1 cm-1 1689±2 1675±2 β-turn for different structures of HPF in PBS are and for cm-1 (α-helix) 1658±1 (a peak is observed on curve 1) (there is a shoulder on curve 1), cm-1 1633±2 (β-sheet) and (this band is masked on curve”

  Rugal 等 - 2007 - Interaction of fibrinogen with nanosilica DOI: 10.2478/s11532-006-0067-4
• Amide confidence 1.0

  “cm-1 C1O, The 1734 band results from BV ring A while that cm-1 C19O.17,23,24 at 1704 is due to ring D The 1689 cm-1 (-)/1682 band is due to amide I (loop/turn) or a (+)”

  Stojkovic 等 - 2014 - FTIR Spectroscopy Revealing Light-Dependent Refold DOI: 10.1021/jz501189t