What absorbs at 1662 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 1662 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 1662 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

• Acetate confidence 1.0

  “Spectroscopy results showed new peak at 1662 for both ENR-25/Titania composite films, which is related to weak C-O stretching vibration.”

  Dahham 等 - 2018 - Studies of ENR-25TiO2 Composites for Electronic M DOI: 10.1088/1742-6596/1019/1/012054
• Carbonyl (C=O) confidence 1.0

  “stretching peak was observed at 1076 In addition, there was also a strong intensity cm-1 peak for the C=O bond at 1662 (Figure S1, Supplementary File).”

  Synthesis, Characterization, Theoretical and Experimental Anticancer Evaluation of Novel Cocrystals of 5-Fluorouracil and Schiff Bases against SW480 Colorectal Carcinoma DOI: 10.3390/pharmaceutics15071929
• Alkyl C-H confidence 1.0

  “CH showed absorption peaks at 1661.58 (Amide I), 3 cm-1 cm-1 1583.56 (-NH bending), 1421.57 (Amide III) [47, 48].”

  Sprayed in-situ synthesis of Polyvinyl alcohol/Chitosan loaded Silver nanocomposite hydrogel for improved antibacterial effects DOI: 10.1016/j.ijbiomac.2019.09.186
• Aromatic ring confidence 1.0

  “The FTIR spectrum of GW2 showed cm-1 𝜋r2]0.5 D characteristic peaks for C-H stretch at 2944 and C=C t0.5, S 4 ∙ = (6) cm-1 [ aromatic stretch at 1662 and NH stretch of amide at”

  Owonubi 等 - 2018 - Characterization and in vitro release kinetics of DOI: 10.1007/s40090-018-0139-2
• Alkene (C=C) confidence 1.0

  “The sharp band at 1662 and cm-1 as 34.18 Å which authenticated the mesoporous structure of are related to the C=C stretching and N--H bend1610 Fe 3O (Huang and Tang 2005).”

  Structural characterization of mesoporous magnetite nanoparticles synthesized using the leaf extract of Calliandra haematocephala and their photocatalytic degradation of malachite green dye DOI: 10.1007/s13204-018-0698-8
• Alkene (C=C) confidence 1.0

  “The hydrocarbon characteristics absorption peaks at 1662 cm-1, 1375 cm-1, and 837 cm-1 relate to the stretching vibrations of C=C bonds, bending cm-1, cm-1, cm-1 1448 1375 and 837 relate to the stretching vibrations of C=C bonds, vibrations”

  Potency of Urea-Treated Halloysite Nanotubes for the Simultaneous Boosting of Mechanical Properties and Crystallization of Epoxidized Natural Rubber Composites DOI: 10.3390/polym13183068
• Alkene (C=C) confidence 1.0

  “Generally, the XRD pattern can change after acid treatment, as verified CH3 groups, and out of plane deformation of =C-H groups were found at 1662 cm-1, 1448 in the study by Makó et al.”

  Selectively Etched Halloysite Nanotubes as Performance Booster of Epoxidized Natural Rubber Composites DOI: 10.3390/polym13203536
• Alkene (C=C) confidence 1.0

  “In cm-1 C=C as well as a band at 1662 related to the stretching of the alkene were observed.”

  Synthesis and Characterization of Novel Resveratrol Butyrate Esters That Have the Ability to Prevent Fat Accumulation in a Liver Cell Culture Model DOI: 10.3390/molecules25184199