What absorbs at 1633 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 1633 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 1633 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

• confidence 1.0

  “The bands at 1633 and 1403 could be assigned to bound cm-1 EPS (Badireddy et al., 2010), which are closely attached to cells.”

  Bakr 等 - 2021 - Predictive performance of auto-aerated immobilized DOI: 10.1016/j.eti.2020.101327
• Amide confidence 1.0

  “Other characteristic peaks of SF protein at-1633 1531 cm-1 cm-1showed 1261 and 665 the presence of amide I (C=O stretching), amide II”

  Dhasmana 等 - 2019 - Silk fibroin protein modified acellular dermal mat DOI: 10.1016/j.msec.2018.12.038
• Hydroxyl (O-H) confidence 1.0

  “LLM confirmed rule peak-group candidate”

  Low-temperature synthesis of Sr2FeMoO6 double perovskite; structure, morphology, and magnetic properties DOI: 10.1016/j.ceramint.2020.03.264
• Amino acid confidence 1.0

  “The protein amino acids absorbance bands for, histidine, at 1633 and salt3Hþ cm-1, n”

  Gupta 等 - 2022 - In vitro cell composition identification of wood d DOI: 10.1098/rsos.201935
• Hydroxyl (O-H) confidence 1.0

  “Vibrations centered cm-1, cm-1 cm-1 at 990 1112 can be assigned to OH stretching modes while at vibration at 1633”

  Mohamed 等 - 2020 - Bio-redox potential of Hyphaene thebaica in bio-fa DOI: 10.1016/j.msec.2020.110890
• confidence 1.0

  “the high intensity is ascribed to the presence digiosin exhibits very strong bands at 1633 due to the 1 of the moiety responsible for this peak (Faraag et al.”

  Resourcefulness of propylprodigiosin isolated from Brevundimonas olei strain RUN-D1 DOI: 10.1186/s13568-023-01579-y
• Amide confidence 1.0

  “Moreover, the band at 1633 cm-1 corresponded to the stretch of the amide C=O [56], and the band at 1395 cm-1”

  Green Synthesis of Silver Nanoparticles for Preparation of Gelatin Films with Antimicrobial Activity DOI: 10.3390/polym14173453
• Alkene (C=C) confidence 1.0

  “Summary of molecular vibration of PBS chromophore (cm-1) Group Wavenumber, 𝝂 700 C-H bending 754 C-H bending of 776 C-H bending 1079 S=O stretching Pre-pro 1218 C-N stretching 1289 C-N stretching 1330 S=O stretching 1402 S=O stretching 1427”

  Power-Dependent Nonlinear Optical Behaviours of Ponceau BS Chromophore at 532 nm via Z-Scan Technique DOI: 10.1016/j.jphotochem.2020.112574