What absorbs at 648 cm⁻¹ in an FTIR spectrum?
A band near 648 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 648 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 |
|---|---|---|---|
| Metal oxygen | 3 | 3 | 1.0 |
| Silicon (Si) | 2 | 2 | 1.0 |
| N h | 2 | 1 | 1.0 |
| Silicon-oxygen (Si-O) | 1 | 1 | 1.0 |
| Alkyl C-H | 1 | 1 | 1.0 |
| Bromine | 1 | 1 | 1.0 |
| Carbon bromine | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
Ranking reflects accumulated literature evidence, not a single fixed rule. Always confirm against your sample context.
Possible materials
| Material | Supporting peaks | Overlapping groups | Cited sources |
|---|---|---|---|
| ZnO NPs | 648, 1664, 875 | Metal oxygen, N h | 1 |
| SnO2 | 648, 2800, 1547 | Metal oxygen | 1 |
| TiO2 | 648, 1700, 1093 | Metal oxygen | 1 |
| TiO2 nanoparticles | 648, 1700, 455 | Metal oxygen, N 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 648 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
-
Metal oxygen confidence 1.0
“LLM confirmed rule peak-group candidate”
Diantoro 等 - 2018 - Control of Dielectric Constant and Anti-Bacterial DOI: 10.1088/1757-899X/367/1/012012 -
Metal oxygen confidence 1.0
“LLM confirmed rule peak-group candidate”
Biocompatible fabrication of TiO2 nanoparticles: Antimicrobial, anticoagulant, antiplatelet, direct hemolytic and cytotoxicity properties DOI: 10.1016/j.inoche.2021.108505 -
Metal oxygen confidence 1.0
“2357 Absorption of CO2 atmosphere Stretching mode of Cu-Fe-Sn-O 648 693 637 641”
Investigation of optical and structural properties of Fe, Cu co-doped SnO2 nanoparticles DOI: 10.1016/j.spmi.2015.03.036 -
C c single bond confidence 1.0
“644.87 and 647.72 and these peaks are the results of C-C bending in CEPTE cm-1”
Raman spectroscopy of Bisphenol ‘S’ and its analogy with Bisphenol ‘A’ uncovered with a dimensionality reduction technique DOI: 10.1016/j.molstruc.2018.08.025 -
Silicon (Si) confidence 1.0
“cm-1 cm-1 1033.11 is attributed to the stretching vibration of Si(Al)-O, the peak at 951.42 is cm-1 attributed to the stretching vibration of Si-O-Fe, the peak at 762.00 is attributed to the cm-1 stretching vibration of Si-Si, the peak at 7”
Effects and Mechanism of Fe3+ on Flotation Separation of Feldspar and Epidote with Sodium Oleate at Natural pH DOI: 10.3390/separations9050110 -
Carbon bromine confidence 1.0
“cm-1 optimum for zinc oxide nanoparticles synthesis I stretching), 601.79 (C-Br stretching), cm-1 cm-1 because of sharper peak at smaller wavelength of 648.08 (C-Br stretching), 759.95 (C-Cl cm-1 352 nm and maximum absorption of 2.151 (Fig.”
Iqtedar 等 - 2020 - Biosynthesis, optimization and characterization of DOI: 10.24275/rmiq/Bio1605 -
Alkyl C-H confidence 1.0
“The ability of cellulolytic enzymes to absorbenciesintherangeof2,933and2,908 degrade cellulose can vary greatly with the physicoto aliphatic C-H stretching and asymmetric CH stretching, 2 cm-1,adramatically chemical characteristics of the s”
Kibedi-Szabo 等 - 2012 - Biodegradation Behavior of Composite Films with Po DOI: 10.1007/s10924-011-0391-4 -
confidence 1.0
“cm-1 cm-1 [C=C]), 1,733 (carbonyl peak), 1,698 (C2=O of guanine or N-H thymine), 1,648 cm-1 (amide I), and 1,543 (amide II) [14-16] Accordingly, we applied PLS regression for calibration and leave-one-out cross validation.”
Macotpet 等 - 2020 - Attenuated total reflection Fourier transform infr DOI: 10.4142/jvs.2020.21.e16
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