What absorbs at 688 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 688 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.

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 688 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

• confidence 1.0

  “The peak cm-1 at 602 can be attributed to terminal oxygen vibration cm-1 of Sn-OH, while the peak appearing at 688 is due to (F1).”

  Synthesis, structural and optical properties of Fe-doped nanocrystalline SnO2 DOI: 10.1007/s10854-017-7018-z
• confidence 1.0

  “In addition to the Ni-O Characterization above bands, the characteristic absorption band of obcm-1 served at 688 corresponds to the stretching vibrations of Ni-O.ItwasobservedthatwiththeadditionofNiOinPMOTFourier transform infrared (FTIR) s”

  Sehgal 和 Narula - 2015 - Structural, morphological, optical, and electrical DOI: 10.1007/s00396-015-3663-z
• confidence 1.0

  “reveals the characteristic vibrational bands at 557, 688, 717, 881, 935 and 1039 The cm-1 vibrational modes at 557 and 717 are assigned to the structural vibrations of yttrium-oxygen cm-1 (Y-O) bonds, the peak at 688 to the stretching mode”

  Luminescence and electron spin resonance studies of narrow-band UVB emitting Gd3+ doped Y2SiO5 nanophosphors synthesized by sol-gel method DOI: 10.1016/j.ijleo.2021.167228
• Silicon (Si) confidence 1.0

  “cm-1 Three medium bands appeared at 688, 752 and 795 were assigned to the deformation modes of AlVI-O-Si bands [21-22].”

  Souissi 等 - 2022 - Synthesis, Thermal Properties and Electrical Condu DOI: 10.21203/rs.3.rs-1294285/v1
• Amide confidence 1.0

  “582cm-1 The peaks at 688 and 900 and have been previously assigned to the α-form of various b nylons16-20 as the amide V and VI, respectively.”

  [gamma]-Crystalline form of nylon-10,10 in nylon-10,10-montmorillonite nanocomposite DOI: 10.1002/pi.1154
• Aromatic ring confidence 1.0

  “Meanwhile, C=C of aromatic ring vibrations were observed at 687.5 the presence of these peak intensities is attributed to pure cinnamaldehyde (Figure 6 (b;”

  Alamier 等 - 2022 - Thermodynamic and Spectroscopic Studies of SDS in DOI: 10.3390/app122312020
• Borate confidence 1.0

  “The absorption peaks at 687.62, 953.71 and 1345.78 attribute to borate network according to Table 3.”

  Facile Synthesis of Calcium Borate Nanoparticles and the Annealing Effect on Their Structure and Size DOI: 10.3390/ijms131114434
• Metal oxygen confidence 1.0

  “1554 - 1427 Zn-O stretching 688 450”

  Fadillah 等 - 2017 - Fabrication and Characterization of ZnO and Li dop DOI: 10.1063/1.4991157