What absorbs at 1670 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 1670 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 1670 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

  “cm-1 cm-1 bands were observed at 1670 , 1516 , 420.48 corresponds to the reducing groups 5 6 (C-O, NH, C-C) present in the bacterial proteins which were responsible for the reduction of 7 8”

  Chandramohan 等 - 2018 - Monodispersed spherical shaped selenium nanopartic DOI: 10.1088/2053-
• Carbonate confidence 1.0

  “intensities increased for all carbonate species for the first Peak DRIFTS absorbance bands at 1670, 1612, 1568, 1440, 1380, 1358, cm-1 40-50 min, and thereafter became constant.”

  Gaur 等 - 2013 - CO oxidation studies over cluster-derived AuTiO2 DOI: 10.1016/j.cattod.2012.10.029
• Acetate confidence 1.0

  “The C=O stretching vibration due to propionamide side chain cm-1 of VB caused the appearance of this intense peak at 1670 [36].”

  Sensitization of ZnO nanoparticle by vitamin B12: Investigation of microstructure, FTIR and optical properties DOI: 10.1016/j.materresbull.2016.07.029
• Acetate confidence 1.0

  “The high C O stretching frequency, and narrow 1670cm-1 12.6cm-1, observed around was assigned to such water clusters are linewidth, full width at half-maximum (FWHM), of”

  Hanawa 等 - 2009 - In situ ATR-FTIR study of bulk CO oxidation on a p DOI: 10.1016/j.electacta.2009.05.061
• Acetate confidence 1.0

  “caribbeana and 1670 for assigned to C=O stretching (secondary amide) when the temperature is under 270 (cid:3)C, for higher temperatures, most of the bands decrease and shift, disappearing for the highest tempera-”

  Juarez-de la Rosa 等 - 2012 - Effects of thermal treatments on the structure of DOI: 10.1007/s10853-011-5878-9
• Carbonyl (C=O) confidence 1.0

  “LLM confirmed rule peak-group candidate”

  Preparation and Characterization of Super-Absorbing Gel Formulated from -Carrageenan–Potato Peel Starch Blended Polymers DOI: 10.3390/polym13244308
• N-O bond confidence 1.0

  “680+Phe-/P 680Phe In the time-resolved spectrum of the P 1668pair (Figures 1a and 4a), no peak was observed at CdO cm-1, where Chl has a keto band (Figures 1670”

  Noguchi 等 - 2001 - Triplet formation on a monomeric chlorophyll in th DOI: 10.1021/bi0019848
• confidence 1.0

  “explicit assignment”

  Purhanudin 和 Awang - 2016 - Formation of chemical bonds and morphological stud DOI: 10.1063/1.4966804