What absorbs at 649 cm⁻¹ in an FTIR spectrum?
A band near 649 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 7 cited sources
Quick answer
A band near 649 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 |
|---|---|---|---|
| Methacrylate | 2 | 2 | 1.0 |
| Acetate | 2 | 2 | 1.0 |
| N-O bond | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| Methoxy (OCH3) | 1 | 1 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Carboxyl (COOH) | 1 | 1 | 1.0 |
| Amide | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| Silicon (Si) | 1 | 1 | 1.0 |
| Adsorbed carbon monoxide | 1 | 1 | 1.0 |
| Borate | 1 | 1 | 1.0 |
| N h | 1 | 1 | 0.9 |
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 |
|---|---|---|---|
| lipids | 649, 1735, 810 | Methacrylate, Acetate | 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 649 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
-
Borate confidence 1.0
“2017).Inalgal cellsbeforebiosorption cm-1 SEM images have clearly shown that Oocystis solitaria samof lithium, the characteristic absorption peak at 649 B-O ples beforeand after lithium biosorption showed different surwhich is assigned to b”
Phycoremediation of lithium ions from aqueous solutions using free and immobilized freshwater green alga Oocystis solitaria: mathematical modeling for bioprocess optimization DOI: 10.1007/s11356-019-05214-x -
Adsorbed carbon monoxide confidence 1.0
“(>99.997 In contrast, as-prepared NiSiBEA sample exhibits a sharp Carbon monoxide purity) was supplied by Linde (>99.0 reduction peak at 649 K and a smaller and broader one at about AG, and nitrogen monoxide purity) was supplied by 785 K (F”
Penkova 等 - 2007 - Effect of the preparation method on the state of n DOI: 10.1021/jp071927p -
confidence 1.0
“bration of Si(Al)-O, the peaks at 787.56 cm-1 and 761.71 cm-1 are assigned to stretching vibration of Si-Si, the peaks at 744.43 cm-1 and 727.85 cm-1 are assigned to stretching vibration of Si-Al(Si), the peaks at 464.98 cm-1 are assigned t”
Effects and Mechanism of Fe3+ on Flotation Separation of Feldspar and Epidote with Sodium Oleate at Natural pH DOI: 10.3390/separations9050110 -
Carbonyl (C=O) confidence 1.0
“The pure NAC molecule showed the main peaks contributed by cm-1), the functional groups of molecules, such as carbonyl -C=O stretching (1,649”
Novel NAC-loaded poly(lactide-co-glycolide acid) nanoparticles for cataract treatment: preparation, characterization, evaluation of structure, cytotoxicity, and molecular docking studies DOI: 10.7717/peerj.4270 -
Hydroxyl (O-H) confidence 1.0
“The broad band between 2900 and cm-1 3600 represents the stretch of the O-H bond, the band at cm-1 1045 indicates a C-O stretch anti-symmetrically coupled to cm-1 the C-C stretch, and the band at 649 is the O-H wag, all of these bands are c”
Research on Misfiring Fault Diagnosis of Engine Based on Wavelet Analysis DOI: 10.25165/j.ijabe.20181105.3748 -
N-O bond confidence 1.0
“Only one thermal decomposition peak appears at 649 C, corresponding to the peak Being an already carbonized material, BC underwent no significant weight loss during the 0.2%/min, T-5% of and the final carbon residue rate was 91.4%.”
Development of Biodegradable Flame-Retardant Bamboo Charcoal Composites, Part II: Thermal Degradation, Gas Phase, and Elemental Analyses DOI: 10.3390/polym12102238 -
N h confidence 0.9
“-NH wagging vibration”
Lu 等 - 2014 - Facile synthesis and characterization of polyethyl DOI: 10.3892/mmr.2014.1906
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