What absorbs at 2125 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 2125 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 2125 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

• Hydroxyl (O-H) confidence 1.0

  “The peak at 2125 represents cm-1 the O-H double bond of graphene.”

  Keyoumu 等 - 2020 - The detailed biological investigations about combi DOI: 10.1016/j.jphotobiol.2019.111666
• Amide confidence 1.0

  “The FTIR findings A strongly suggested that these two polymers are thermodynamic incompatible as amide I peak cmwas increased in the BLG-BSG mixed system and CN stretching peak was observed at 2125 * Corresponding author.”

  Rafe 和 Razavi - 2015 - Effect of Thermal Treatment on Chemical Structure DOI: 10.1080/10942912.2014.999864
• Silicon hydride confidence 1.0

  “intensity of the observed Si-H peak at 2125 The increase in oxide levels after the reflux step can not be attributed to ethoxy capping due to the absence of ethanol and the shape of the peak, but the”

  The effect of alkyl chain length on the level of capping of silicon nanoparticles produced by a one-pot synthesis route based on the chemical reduction of micelle DOI: 10.1007/s11051-013-1425-8
• confidence 0.9

  “Band at 2125 cm-1 attributed to Au-H species.”

  Fundamental Aspects of Ceria Supported Au Catalysts Probed by In Situ/Operando Spectroscopy and TAP Reactor Studies DOI: 10.1002/cphc.202100027
• confidence 0.9

  “CO adsorption on FTIR spectra at 2125 cm-1”

  Converting waste PET plastics into automobile fuels and antifreeze components DOI: 10.1038/s41467-022-31078-w
• confidence 0.8

  “Peak upon binding to Mb.”

  Blouin 和 Olson - 2010 - The Stretching Frequencies of Bound Alkyl Isocyani DOI: 10.1021/bi100172c.
• Nitrile confidence 0.8

  “Text states 'two peaks (2125 and 2200 cm-1) ... corresponding to C≡N, C=N, C-N bonds'.”

  Bonding structure and optical properties of a-CNx:H films deposited in CH4-NH3 system DOI: 10.1016/j.vacuum.2009.04.055