What absorbs at 728 cm⁻¹ in an FTIR spectrum?
A band near 728 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 728 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 |
|---|---|---|---|
| Alkyl C-H | 4 | 4 | 1.0 |
| C c single bond | 2 | 2 | 1.0 |
| Ring structure | 2 | 1 | 1.0 |
| Lipid | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Amide | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Phosphate (PO4) | 1 | 1 | 1.0 |
| Methoxy (OCH3) | 1 | 1 | 1.0 |
| Methacrylate | 1 | 1 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| Acetate | 1 | 1 | 1.0 |
| Silicon silicon | 1 | 1 | 1.0 |
| Silicon (Si) | 1 | 1 | 1.0 |
| Nitrate | 1 | 1 | 1.0 |
| N-O 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 |
|---|---|---|---|
| cellulose | 728, 1735, 1650 | Alkyl C-H | 3 |
| hemicellulose | 728, 1730, 897 | Alkyl C-H | 2 |
| lignin | 728, 1035, 1510 | Alkyl C-H | 2 |
| PET | 728, 1408, 800 | Alkyl C-H | 1 |
| graphene oxide | 728, 1150, 3400 | Alkyl C-H | 1 |
| collagen | 728, 1408, 1660 | 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 728 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
-
N-O bond confidence 1.0
“The absorption bands 1413 cm-1 3-, cm-1 cm-1 at 815.25 and 728.12 were assigned to the N-O bending vibration of NO and to C-N at 815.25 cm-1 and 728.12 cm-1 were assigned to the N-O bending vibration of NO3-, and to C-N stretching from the”
Effect of Ratio in Ammonium Nitrate on the Structural, Microstructural, Magnetic, and AC Conductivity Properties of BaFe12O19 DOI: 10.3390/ma11112190 -
Alkyl C-H confidence 1.0
“Upon functionalization with various alkylamines corresponding to the C-H stretching vibration of the alkyl chain (CH2), together with a peak around cm-1 γ-ray through irradiation, the peaks around 2920-2852 appeared, corresponding to the C-”
Daud 等 - 2017 - Functionalizing Graphene Oxide with Alkylamine by DOI: 10.3390/nano7060135 -
Silicon (Si) confidence 1.0
“The peaks at 1139.24 cm-1 and 1095.99 cm-1 are assigned to stretching vibration of Si-O, the peaks at 1031.25 cm-1 and 1008.16 cm-1 are assigned to stretching vibration of Si(Al)-O, the peaks at 787.56 cm-1 and 761.71 cm-1 are assigned to s”
Effects and Mechanism of Fe3+ on Flotation Separation of Feldspar and Epidote with Sodium Oleate at Natural pH DOI: 10.3390/separations9050110 -
Acetate confidence 1.0
“vibration of the C-H out of plane from the aromatic ring, at 800 cm-1 attributed to (C=O+CCO) cm-1 cm-1 ν(C=C) the oxyethylene groups, at 1020 cm-1 for ν(C=C) of the aromatic ring, at 875 cm-1 showing the groups, at 1020 for of the aromatic”
Drobota 等 - 2020 - Preparation and Characterization of Electrospun Co DOI: 10.3390/ma13183961 -
Phosphate (PO4) confidence 1.0
“s By the comparison of the IR spectrum of the TCP powder before and after the calcinations cm-1, at T=900°C presented on figure 3, we notice the appearance of the band located at 728 42attributed to the grouping HPO (P-OH elongation) and th”
Ghamri 等 - 2023 - Effect of thermal treatment on the structural, mor DOI: 10.15251/DJNB.2023.182.531 -
C c single bond confidence 1.0
“Pristine Composite Zn-N absent 664 groups stretching (compl) absent 728 Out-of-plane deformation of H-atoms (compl) C-C C-N absent 851 and deformation (compl) C-O-C,C-C-O C-C-H 897 disappear and deformation and stretching (cell)”
Mikhailidi 等 - 2020 - HIGHLY POROUS HYBRID COMPOSITE HYDROGELS BASED ON DOI: 10.5772/intechopen.80898 -
Lipid confidence 1.0
“sample through the vibrational and valence group peaks that belong to the structural sample through the vibrational and valence group peaks that belong to the structural cm-1), cm-1) components based on rosin (3443, 2939 and 2879 wax (2833,”
Sandu 等 - 2023 - Authentication of a Stradivarius Petite Violin T DOI: 10.3390/app -
C c single bond confidence 1.0
“The addition of toluene on poplar caused three cm-1 cm-1 cm-1 bands including 3069 for C-H stretching, 1497 for C-C stretching, and 728 for C-H out”
Zhuang 等 - 2020 - Observation of Potential Contaminants in Processed DOI: 10.3390/app10124345
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