What absorbs at 1660 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 1660 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 1660 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

• N h confidence 1.0

  “PG100 film at 2856 The carbonyl C=O double bond stretching mode dominates the amide I band, with contributions from the CN stretch, CCN deformation and in-plane NH bending modes and is mostly found in the region of 1660 cm-1 to 1620 cm-1, w”

  Application of Poultry Gelatin to Enhance the Physicochemical, Mechanical, and Rheological Properties of Fish Gelatin as Alternative Mammalian Gelatin Films for Food Packaging DOI: 10.3390/foods12030670
• Bromine confidence 1.0

  “cm-1is (cid:3) at 1435 assigned to the 4(F) bending mode of Brönsted acid (cid:3) bound ammonium ions [49,51,53], but the corresponding sites 2 cm-1 (E) vibration mode is absent at 1660 [59].”

  Low-temperature selective catalytic reduction of NO with NH3 over V/ZrO2 prepared by flame-assisted spray pyrolysis: Structural and catalytic properties DOI: 10.1016/j.apcatb.2012.08.012
• Alkene (C=C) confidence 1.0

  “The band at 1660 can be attributed to the -C=Cstretching vibration of alkenes cm-1 [36].”

  Mesoporous magnetite nanoparticles synthesis using the Peltophorum pterocarpum pod extract, their antibacterial efficacy against pathogens and ability to remove a pollutant dye DOI: 10.1016/j.molstruc.2018.10.042
• Carbonyl (C=O) confidence 1.0

  “Young and Chang [15] studied the FTIR changes of PMR-15 after thermal spiking and also observed this change along with the ingrowth cm(cid:2)1, of peaks at 1660 and 930 both arising from the bridging carbonyl group.”

  Fox 等 - 2004 - Investigation of failure mechanisms in aged aerosp DOI: 10.1016/j.engfailanal.2003.05.010
• Alkene (C=C) confidence 1.0

  “The intense FT-IR peaks at cm-1 1660 and 3461 of GQDs spectrum reveals the presence of a C=C and an O-H stretching, in that order.”

  Gebreegziabher 等 - 2020 - Polyaniline-graphene quantum dots (PANI-GQDs) hybr DOI: 10.1007/s42823-019-00064-6
• Acetate confidence 1.0

  “The first was at 1717 which cm-1 refers to (C O) group of a free aldehyde end of glutaraldehyde, and another peak was at 1660 Keywords: referring to (C N ) group.”

  Covalent immobilization of Enterococcus faecalis Esawy dextransucrase and dextran synthesis DOI: 10.1016/j.ijbiomac.2015.09.076
• Amide confidence 1.0

  “Moreover, the FTIR Electron irradiation cm-1, spectra showed higher intensities of the peaks at 1660 and 1720 which are attributed to stretching rate effect Dose vibrations of amide C O and ketone/acid C O, at lower dose rates.”

  Dose rate effects on shape memory epoxy resin during 1 MeV electron irradiation in air DOI: 10.1016/j.jmst.2020.06.020
• Amide confidence 1.0

  “The peaks at 1692 1687 (-) cm-1 77 and 100 K are enlarged by 1/0.36 and 1/0.64, respectively, and 1673 can be attributed to the amide I vibrations (+) (-) to normalize the population of D447 photoconverted to S390 of turn structure, and the”

  Iwata 等 - 2003 - Light-induced structural changes in the LOV2 domai DOI: 10.1021/bi0345135