What absorbs at 678 cm⁻¹ in an FTIR spectrum?
A band near 678 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 5 cited sources
Quick answer
A band near 678 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 |
|---|---|---|---|
| Silicon-oxygen (Si-O) | 2 | 1 | 1.0 |
| C-S single bond | 2 | 1 | 1.0 |
| Metal oxygen | 2 | 1 | 1.0 |
| Carbon bromine | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| Alkyl C-H | 1 | 1 | 0.8 |
| Silicon (Si) | 1 | 0 | 1.0 |
| Siloxane (Si-O-Si) | 1 | 0 | 1.0 |
Ranking reflects accumulated literature evidence, not a single authoritative rule. Always confirm against your sample context.
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 678 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
-
confidence 1.0
“2014), whereas two small bands A cm-1 positioned at 678 and 618 are linked to Ag-O (Kumar and Rani 2013;”
Haq 等 - 2018 - Fabrication of pure and moxifloxacin functionalize DOI: 10.1016/j.jphotobiol.2018.07.011 -
C c single bond confidence 1.0
“24 25 cm-1 A small peak observed at 678 is C-C out of plane ring deformation or C-H rocking [28].”
Velhal 等 - 2018 - Structural, electrical and microwave properties of DOI: 10.1088/2053-1591/aadaf7 -
C-S single bond confidence 1.0
“In cm-1 cm-1 this Raman spectra peaks at 678 and 713 are attributed to C-S symmetric and cm-1 antisymmetric stretches, and the peak at 1000 is assigned to the S=O stretch.”
Origin of Defects and Positron Annihilation in Hybrid and All-Inorganic Perovskites DOI: 10.1021/acs.chemmater.1c03540 -
Silicon-oxygen (Si-O) confidence 1.0
“styreneSi-O-Si), Si-CH However, the analysis suggests that the material could be 3), 1101 (asymmetric stretching of 1068 (asymmetric Si-O-Si), Si-O-Si), stretching of 806 (symmetric stretching of 678 butadienerubber(SBR)becausesignalsofsuch”
Non-invasive identification of plastic materials in museum collections with portable FTIR reflectance spectroscopy: Reference database and practical applications DOI: 10.1016/j.microc.2015.07.016 -
Carbon bromine confidence 1.0
“LLM confirmed rule peak-group candidate”
Setyawati 等 - 2017 - Synthesis and Characterization of Novel Benzohydra DOI: 10.1063/1.4978194
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