What absorbs at 663 cm⁻¹ in an FTIR spectrum?
A band near 663 cm⁻¹ can point to several functional groups. Below are the most likely assignments, ranked by how much published evidence supports each — every one traceable to literature (DOI) and cross-validated against our 130,000+ reference spectra and knowledge graph.
Backed by 8 cited sources
Quick answer
A band near 663 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
| Functional group | Supporting facts | Cited sources | Top confidence |
|---|---|---|---|
| Hydroxyl (O-H) | 2 | 2 | 1.0 |
| Silicon-oxygen (Si-O) | 2 | 2 | 1.0 |
| Silicon (Si) | 2 | 2 | 1.0 |
| Carbon bromine | 2 | 2 | 1.0 |
| Secondary amine | 2 | 2 | 1.0 |
| C n single bond | 2 | 2 | 1.0 |
| Amide | 2 | 2 | 1.0 |
| Metal oxygen | 1 | 1 | 1.0 |
| Bromine | 1 | 1 | 1.0 |
| Chlorine | 1 | 1 | 1.0 |
| Siloxane (Si-O-Si) | 1 | 1 | 1.0 |
| Thiol | 1 | 1 | 1.0 |
| Carboxyl (COOH) | 1 | 1 | 0.8 |
Ranking reflects accumulated literature evidence, not a single authoritative rule. Always confirm against your sample context.
Possible materials
| Material | Supporting peaks | Overlapping groups | Cited sources |
|---|---|---|---|
| Silica | 663, 1100, 1080 | Silicon-oxygen (Si-O), Silicon (Si), Hydroxyl (O-H) | 1 |
| copper oxide | 663, 624, 1686 | Hydroxyl (O-H) | 1 |
| hydroxyapatite | 663, 1620, 1639 | Hydroxyl (O-H) | 1 |
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 663 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
-
Thiol confidence 1.0
“The second silicate bands are 4 cm-1 in C-S-H broadly characterized as O-Si-O deformation or bending modes, which occur near 451 470cm-1 cm-1 667cm-1 and in C-A-S-H and the band 663 or is due to Si-O-Si bending vibrations.”
He 等 - 2011 - Morphology and Structure of Aluminum Substituted C DOI: 10.4028/www.scientific.net/AMR.287-290.1193 -
confidence 1.0
“Peak at 663 Tensile tests were performed according to ASTM D638 corresponds to the C-Cl stretching in PVC chains.”
Ibrahim 等 - 2011 - A study of poly vinyl chloridepoly(butylene adipa DOI: 10.1007/s10965-010-9486-1 -
Carbon bromine confidence 1.0
“The intense bands situated at about 663 and 1025cm-1 of wavelength were assigned to the stretching vibrational movement of C-Br and”
Jing 等 - 2019 - Biosynthesis of copper oxide nanoparticles and the DOI: 10.1016/j.jphotobiol.2019.111557 -
Amide confidence 1.0
“pneumonia were observed by SEM based on a method reported 663cm-1 C-N C-Br ∼105CFU/mL are due to and stretching vibrational motions.”
Biologically synthesized copper oxide nanoparticles enhanced intracellular damage in ciprofloxacin resistant ESBL producing bacteria DOI: 10.1016/j.micpath.2018.12.017 -
Hydroxyl (O-H) confidence 1.0
“cm-1 Analysis of deuterated samples [50] shows that the relatively sharp peak at 663 is due to the O-H Analysis of deuterated samples [50] shows that the relatively sharp peak at 663 cm-1 is due to the Olibration (see inset in Figure 4).”
Baldassarre 等 - 2020 - Crystal Chemistry and Luminescence Properties of E DOI: 10.3390/cryst10040250 -
confidence 1.0
“The strong bonds between 981.1 cm-1 and 662.7 cm-1 stretching with halogen groups.”
Synthesis and Characterization of Sulfur Nanoparticles of Citrus limon Extract Embedded in Nanohydrogel Formulation: In Vitro and In Vivo Studies DOI: 10.3390/gels9040284 -
confidence 1.0
“is triuoroacetate electrostatic interaction of lanthanum and triarticle cm-1 Si-O-Si La-O-Si 663 assigned to & bond vibrations, chloroacetate with the silica support material, which converts Article.”
Silica supported lanthanum trifluoroacetate and trichloroacetate as an efficient and reusable water compatible Lewis acid catalyst for synthesis of 2,4,5-triarylimidazoles via a solvent-free green approach DOI: 10.1039/d2ra07021a -
Hydroxyl (O-H) confidence 1.0
“Analysis of deuterated samples [56] shows cm-1 that the relatively sharp peak at 663 is due to the O-H libration.”
Paterlini 等 - 2020 - Characterization and Luminescence of Eu3+- and Gd3 DOI: 10.3390/cryst10090806
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