What absorbs at 690 cm⁻¹ in an FTIR spectrum?
A band near 690 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 690 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 | 6 | 6 | 1.0 |
| N h | 6 | 5 | 1.0 |
| Alkyl C-H | 4 | 4 | 1.0 |
| Amide | 4 | 4 | 1.0 |
| Chlorine | 4 | 3 | 1.0 |
| Methoxy (OCH3) | 3 | 3 | 1.0 |
| Methacrylate | 3 | 3 | 1.0 |
| Acetate | 3 | 3 | 1.0 |
| C-O single bond | 3 | 3 | 1.0 |
| Hydroxyl (O-H) | 3 | 3 | 1.0 |
| Hydrogen bond | 2 | 2 | 1.0 |
| Aromatic ring | 2 | 2 | 1.0 |
| Secondary amine | 2 | 2 | 1.0 |
| C n single bond | 2 | 2 | 1.0 |
| Silicon-oxygen (Si-O) | 2 | 1 | 1.0 |
| Silicon (Si) | 2 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| Siloxane (Si-O-Si) | 1 | 1 | 1.0 |
| Sulfur heterocycle | 1 | 1 | 1.0 |
| Carboxyl (COOH) | 1 | 1 | 1.0 |
| Carbonate | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| S eq o | 1 | 1 | 1.0 |
| Metal hydroxyl | 1 | 1 | 1.0 |
| C-S single bond | 1 | 1 | 1.0 |
| Imide | 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 |
|---|---|---|---|
| gold nanoparticles | 690, 1638, 3252 | Amide, Alkyl C-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 690 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
-
Alkyl C-H confidence 1.0
“All analytical experiments were carried out in triplicate expericm(cid:1)1 The band obtained at 690 revealed C-H stretching vibrations.”
Green synthesis and characterization of gold nanoparticles using endophytic fungi Fusarium solani and its in-vitro anticancer and biomedical applications DOI: 10.1016/j.sjbs.2019.12.026 -
Acetate confidence 1.0
“3d), showedtherelationshipsbetweenpeakheightsat~690,~760, C_O 380 394 indicating a predominant absorption of at 1660 to 1640/ ~890/cm and SOC concentration.”
Yu 等 - 2018 - Fast screening compositions of PM2.5 by ATR-FTIR DOI: 10.1016/j.jes.2017.11.021 -
Amide confidence 1.0
“Fortes absorções relacionadas à banda C-H aparecem em 2940, 2860 e 1460 A fase cm-1, cm-1 cm-1, das poliamidas apresenta picos nas regiões de 929 959 (CONH da fase cristalina ) e 1200 e cm-1, por volta de 690 aparece uma banda referente”
de Medeiros 等 - 2017 - Asymmetric hybrid microporous membranes influence DOI: 10.1590/S1517-707620170002.0144 -
Imide confidence 1.0
“LLM confirmed rule peak-group candidate”
Adzima 等 - 2008 - Rheological and Chemical Analysis of Reverse Gelat DOI: 10.1021/ma801863d. -
confidence 1.0
“cm-1 presence of BaTi 4O The absorption mode appearing at ~ 690 represents the Ti-O stretching 9 structure23,24, mode of the octahedral group in complex perovskite as this mode appears only in BaTi 4O ceram9”
Structural, optical and microwave dielectric properties of Ba(Ti1−xSnx)4O9, 0 ≤ x ≤ 0.7 ceramics DOI: 10.1038/s41598-021-97584-x -
confidence 1.0
“The impedance ́ ́ Ct et-H(Me) Ct et-H(aromp-sub) 690cm-1 ] measurements were taken in an open circuit using two at becomes very low note that the band C-Cl electrode configurations with signal amplitude of 50mV comparedtothatcorrespondingto”
Ammari 等 - 2015 - Structure and Electrical Study of New Chemically M DOI: 10.1155/2015/280325 -
C-S single bond confidence 1.0
“FTIR analysis of the dried seaweed and colloid extracts from Bonds/Assignments (cm-1) Wavelength Numbers 609 C-S stretching vibrations (agar) 690 3,6anhydro-L-galactose (agar)”
Extraction and Analysis of Compounds with Antibacterial Potential from the Red Alga Grateloupia turuturu DOI: 10.3390/jmse7070220 -
Metal oxygen confidence 1.0
“One visible shoulder peak at ~717 emerged, which is the absorption band of the Fe-O in the FH [26], at the expense of the shoulder peak located at cm-1 690 in fresh precursors.”
Effects of Potassium Loading over Iron–Silica Interaction, Phase Evolution and Catalytic Behavior of Precipitated Iron-Based Catalysts for Fischer-Tropsch Synthesis DOI: 10.3390/catal12080916
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