What absorbs at 639 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 639 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.

가능한 작용기 할당

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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 639 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.

이 할당의 배경이 되는 문헌

• Hydroxyl (O-H) 신뢰도 1.0

  “2932 O-H stretching alcohol 639 C-Br stretching halo compound”

  The Antifungal Properties of Tamarix aphylla Extract against Some Plant Pathogenic Fungi DOI: 10.3390/microorganisms11010127
• 신뢰도 1.0

  “It was 1089.6cm-1 (S=O stretching vibration) and 1136.8, and also observed that some peaks shown by pure etoricoxib 639.22009cm-1 (C-Cl stretching vibra834.0, 777.1, and were absent, and the intensity of peaks of these etoricoxib tion).”

  Das 等 - 2011 - Solubility and dissolution enhancement of etoricox DOI: 10.5402/2011/819765
• 신뢰도 1.0

  “Raman spectra of PVC showed absorption peaks s c cm-1 at 639 and 697 that are assigned to C-Cl stretching vibrations and absorbance peaks r”

  Kundu 等 - 2021 - Identification and removal of microand nano-plas DOI: 10.1016/j.cej.2021.129816.
• Phosphate (PO4) 신뢰도 1.0

  “We 638 assume these complexes are protonated based on the existence of characteristic P-O-H bands at cm-1, 639 972±7 and 957±8 respectively (Elzinga and Kretzschmar, 2013).”

  Rosello 等 - 2023 - Investigating phosphate-adsorption behaviour on a DOI: 10.1071/sr22011