What absorbs at 1628 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 1628 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 1628 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

  “Obvious Fourier transform infrared cm-1, cm-1, (FTIR) spectra for the GT extract were observed, showing absorption bands at 3401 1628 cm-1, and 1029 corresponding to O-H/N-H, C=O, and C-O groups, respectively.”

  Aziz 等 - 2017 - From Insulating PMMA Polymer to Conjugated Double DOI: 10.3390/polym9110626
• confidence 1.0

  “The cm-1 180 peaks around 1628, 1512, 1384, 1258, 1028 and 688 indicating the possible presence of 181 N-H bend, C-C, C-H, C-N stretch and =C-H groups of amines, aromatics, alkanes, and 182 aliphatic amines (Irshad et al., 2017;”

  Bio-inspired synthesis of flower shaped iron oxide nanoparticles (FeONPs) using phytochemicals of Solanum lycopersicum leaf extract for biomedical applications DOI: 10.1016/j.bcab.2020.101698
• Hydroxyl (O-H) confidence 1.0

  “The peak at 1710 was standard[24] according to the ASTM from the data attributed to the C = O stretching vibrations in the of three-point bend test at 1 month storage time by cm-1 carboxylic group and the peak at 1628 was drawing a tangent”

  Fareed 和 Stamboulis - 2014 - Nanoclay addition to a conventional glass ionomer DOI: 10.4103/1305-7456.143619
• Hydroxyl (O-H) confidence 1.0

  “centered at 3425 The absorption peaks centered at cm-1 1628 and 1384 is ascribed to O-H bending vibrations on the surface of nano-composite.”

  Photo-catalytic activity of highly efficient binary Mn–Fe nano composite oxides for degradation of cresol fast violet: phase formation and band gap study DOI: 10.1007/s10854-017-7206-x
• Carboxyl (COOH) confidence 1.0

  “The band at 1627.92 indicates the presence of a -COOH group cm-1 and the band on 1519.91 indicate of -NH group.”

  Hastuti 和 Assya'adha - 2020 - Synthesis and Characterization of Chitosan Membran DOI: 10.1088/1757-899X/833/1/012068
• Alkene (C=C) confidence 1.0

  “The absorption bands situated at about 1628 and of wavelength were assigned to the C=C as well as O-H stretching vibrational movements.”

  Jing 等 - 2019 - Biosynthesis of copper oxide nanoparticles and the DOI: 10.1016/j.jphotobiol.2019.111557
• Water (H2O) confidence 1.0

  “cm-1 well equivalent with the rutile structure of SnO The band at 1628 may be due to the bending 2 There are new diffraction peaks observed with the values of vibration of the hydrogen-bonded water molecules within the”

  Hybrid structure of biotemplate-zinc-tin oxide for better optical, morphological and photocatalytic properties DOI: 10.1088/1361-6641/aa577c
• Water (H2O) confidence 1.0

  “3 A (3) C OeH In IR spectrum the stretching and deformation vibration peaks 1628cm-1 assigned at 3430 and are due to the adsorbed water moleis the absorbance control, and A is the sample absorWhere, A C S”

  Green synthesis of ionic liquid assisted ytterbium oxide nanoparticles by Couroupita guianensis abul leaves extract for biological applications DOI: 10.1016/j.jece.2020.103992