What absorbs at 1648 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 1648 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 1648 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

  “The results showed major changes in lipids (vibration 1744 assigned to C=O stretching) cm-1 cm-1 and proteins (vibrations 1648 assigned to C=O stretching of amide I and 1548 assigned to N-H bending and C-N stretching in amid II).”

  Fourier transform infrared microspectroscopy detects biochemical changes during C. elegans lifespan DOI: 10.1016/j.vibspec.2019.04.005
• Aromatic ring confidence 1.0

  “prostrata were indicated at cm-1 cm-1 cm-1 3852 (H-H weak peak), 3138 (Aromatic C-H stretch), 1648 (Aromatic ring stretch), cm-1 cm-1 1522 (Aromatic nitro compounds) and 1082 (organic siloxane or silicone (Si-O-Si) (Figure 2b).”

  An Investigation of the Cytotoxicity and Caspase-Mediated Apoptotic Effect of Green Synthesized Zinc Oxide Nanoparticles Using Eclipta prostrata on Human Liver Carcinoma Cells DOI: 10.3390/nano5031317
• confidence 1.0

  “cm-1 cm-1 Furthermore, as shown in Figure 3, the peaks at (iv) 1648 and (v) 1564 represent the electrolyte's carboxamide and amine bands, respectively [55,56].”

  Characteristics of Plasticized Lithium Ion Conducting Green Polymer Blend Electrolytes Based on CS: Dextran with High Energy Density and Specific Capacitance DOI: 10.3390/polym13213613
• Silicon (Si) confidence 1.0

  “The spectrum of cm(cid:1)1 the holtite II crystals (1.66(cid:1)1.67 and H4 also shows a small peak at 1648 due to A˚), 1.65(cid:1)1.68 reflecting the difference in Si site bending of non-structural H 2O (Voloshin et al.,”

  Groat 等 - 2009 - The crystal chemistry of holtite DOI: 10.1180/minmag.2009.073.6.1033
• Alkene (C=C) confidence 1.0

  “other peaks of AV films 1647.88 cm-1 and 1149.37 showed the presence of substituted alkene, C-H rock with phenolic group and C-H wag with”

  Synthesis and characterization of eco-friendly bioplastic from low-cost plant resources DOI: 10.1007/s42452-019-1460-x
• Amide confidence 1.0

  “The amide I bands pertain tumors.50 cm-1 to the 1648 band which shifts to a lower wavenumber Viability of cells gives important information about the and intensity in cancer cells than in normal cells.”

  Lane 和 Seo - 2012 - Attenuated Total Reflectance Fourier Transform Inf DOI: 10.1166/jnn.2012.6582
• Amide confidence 1.0

  “Moderate exposure of the cm(cid:0) 1), O-H BRG peaks, displaying stretching (band A, 3389 amide I hydrophobic protein groups promoted the protein-oil interaction, cm(cid:0) 1), C¼O N-H (band B, stretching, 1648 amide II (band C, bending, co”

  Effect of different carbohydrates on the functional properties of black rice glutelin (BRG) modified by the maillard reaction DOI: 10.1016/j.jcs.2020.102979
• Alkyl C-H confidence 1.0

  “cm-1 and C-H stretching C=C peak appeared at 1648 Fig 1.”

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