What absorbs at 1664 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 1664 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 1664 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

• Alkyl C-H confidence 1.0

  “The incorporation of PAN chains was further supported cm.-1 cm-1 by methylene C-H bending peak at 1664 CH bending is seen at 1453 (asym) and 3”

  Synthesis of Aloevera/Acrylonitrile based Nanoparticles for targeted drug delivery of 5-Aminosalicylic acid DOI: 10.1016/j.ijbiomac.2017.08.085
• Acetate confidence 1.0

  “2(b) shows the C=O peak shifting 1664 was huge.”

  Mohammed 等 - 2020 - Thermal and Structure Analysis Based on Exfoliatio DOI: 10.22146/ijc.40872
• Amide confidence 1.0

  “Images generated from the normalized intensity of the second derivative of the FTIR cm-1) cm-1): and the shifted protein amide I band (1664 (d, e) for controls (skin spectra, centered around the hydroxamate amide II band (1562”

  High-Sensitivity Permeation Analysis of Ultrasmall Nanoparticles Across the Skin by Positron Emission Tomography DOI: 10.1021/acs.bioconjchem.1c00017
• Acetate confidence 1.0

  “Three Gaussian-Lorentzian sums were considered in the curve fitting of the carbonyl region (Figure 6) at 1729 cm-1, 1710 cm-1 and 1664 cm-1, where they corresponded to C=O free urethane, C=O H-bonded urethane and C=O urea [4], respectively.”

  Effects of NCO/OH Ratios on Bio-Based Polyurethane Film Properties Made from Acacia mangium Liquefied Wood DOI: 10.3390/polym15051154
• Carbonyl (C=O) confidence 1.0

  “The AG had a molecular weight of acterized bya band at 1664 whereas carbonyl stretch of acid inCHOL-ALwasconfirmedbyabandat1714cm(cid:1)1Carbonylstretch reports.21 around 13 KDa as per the literature Increase in the mocm(cid:1)1.”

  Cholesterol anchored arabinogalactan for asialoglycoprotein receptor targeting: synthesis, characterization, and proof of concept of hepatospecific delivery DOI: 10.1016/j.carres.2015.03.003
• Amide confidence 1.0

  “The individual peak at 1664 cm-1 1664 was noted as an amide I band (C=O), and a C=C ring vibration of the polyamide cm-1 was noted as an amide I band (C=O), and a C=C ring vibration of the polyamide layer cm-1 cm-1 layer at 1609 [41] appear”

  Autopsy of Used Reverse Osmosis Membranes from the Largest Seawater Desalination Plant in Oman DOI: 10.3390/membranes12070671
• Amide confidence 1.0

  “Peak at cm-1 cm-1 1664 is indicative of C = O stretching of amide-I group and peak at 1610 (N-H cm-1 bending of amide-II).”

  Development, characterization and In-vitro evaluation of guar gum based new polymeric matrices for controlled delivery using metformin HCl as model drug DOI: 10.1371/journal.pone.0271623
• Acetate confidence 1.0

  “The spectrum in Figure 5b cm-1 corresponds with typical pristine gelatin fibers, with C=O stretching vibration appearing which determine the PL in the orange-red region, had been passivated during GNF@ZnO at 1664 cm-1, demonstrated by the a”

  Babayevska 等 - 2021 - Fabrication of Gelatin-ZnO Nanofibers for Antibact DOI: 10.3390/ma14010103