What absorbs at 780 cm⁻¹ in an FTIR spectrum?
A band near 780 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 320,000+ reference spectra and knowledge graph.
Backed by 7 cited sources
Quick answer
A band near 780 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) | 12 | 11 | 1.0 |
| Alkyl C-H | 10 | 9 | 1.0 |
| Silicon carbon | 5 | 3 | 1.0 |
| Methacrylate | 4 | 4 | 1.0 |
| Acetate | 4 | 4 | 1.0 |
| Ring structure | 4 | 4 | 1.0 |
| Carboxyl (COOH) | 4 | 4 | 1.0 |
| Metal oxygen | 4 | 4 | 1.0 |
| Silicon (Si) | 3 | 3 | 1.0 |
| Siloxane (Si-O-Si) | 3 | 3 | 1.0 |
| Methoxy (OCH3) | 3 | 3 | 1.0 |
| C-O single bond | 3 | 3 | 1.0 |
| Aromatic ring | 3 | 3 | 1.0 |
| Alkene (C=C) | 3 | 2 | 1.0 |
| C c single bond | 2 | 2 | 1.0 |
| Amide | 2 | 2 | 1.0 |
| Secondary amine | 2 | 2 | 1.0 |
| Phosphate (PO4) | 2 | 1 | 1.0 |
| Boron nitrogen | 2 | 1 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Metalloid oxygen | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Phosphorus | 1 | 1 | 1.0 |
| Urethane | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| N h | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| Silanol (Si-OH) | 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 |
|---|---|---|---|
| SiC | 780, 791, 614 | Silicon carbon, Silicon-oxygen (Si-O) | 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 780 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
-
C-O single bond
- Reported band
- 780 cm-1
- Assignment
- C-O single bond
- Material / context
- —
-
Boron nitrogen
- Reported band
- 780 cm-1
- Assignment
- Boron nitrogen
- Material / context
- B4C/BCN/c-BN multilayered thin; c-BN multilayered thin; B4C/BCN/c-BN multilayered thin films
-
Silicon carbon
- Reported band
- 780 cm-1
- Assignment
- Silicon carbon
- Material / context
- SiC; Si nanocrystals
-
Siloxane (Si-O-Si)
- Reported band
- 780 cm-1
- Assignment
- Siloxane (Si-O-Si)
- Material / context
- sisal; hemp
-
Silanol (Si-OH)
- Reported band
- 780 cm-1
- Assignment
- Silanol (Si-OH)
- Material / context
- sol-gel coated hemp shiv
-
Silicon carbon
- Reported band
- 780 cm-1
- Assignment
- Silicon carbon
- Material / context
- silicon carbide; Silicon Carbide in Rhombohedral Form
-
Ring structure
- Reported band
- 780 cm-1
- Assignment
- Ring structure
- Material / context
- carbon nitrides
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