What absorbs at 726 cm⁻¹ in an FTIR spectrum?
A band near 726 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 726 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 | 5 | 5 | 1.0 |
| Methoxy (OCH3) | 3 | 3 | 1.0 |
| Methacrylate | 3 | 3 | 1.0 |
| Acetate | 3 | 3 | 1.0 |
| C-O single bond | 2 | 2 | 1.0 |
| Methyl | 1 | 1 | 1.0 |
| Borate | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| Metal oxygen | 1 | 1 | 0.9 |
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 |
|---|---|---|---|
| PET | 726, 1408, 800 | Methacrylate, Acetate, Alkyl C-H | 1 |
| polyester | 726, 1700, 1250 | Alkyl C-H, Methacrylate, Acetate | 1 |
| collagen | 726, 1408, 1660 | Methacrylate, Acetate, Alkyl C-H | 1 |
| HDPE | 726, 1369, 1216 | Alkyl C-H, Methacrylate, Acetate | 1 |
| LDPE | 726, 1720, 1737 | Alkyl C-H, Methacrylate, Acetate | 1 |
| soil | 726, 575, 1240 | Alkyl C-H, 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 726 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
“LLM confirmed rule peak-group candidate”
Bahadi 等 - 2021 - Synthesis and Characterization of Green Biodegrada DOI: 10.33263/BRIAC116.1435914371 -
Alkyl C-H confidence 1.0
“cm-1 Peaks at 2927-2856 indicate the -CH 2and -CH scissoring of OA and EOA, as shown in Figure 1, while the 3 cm-1 absorption bands at 726 indicate C-H vibration.”
Bahadi 等 - 2021 - Synthesis and characterization of palm oleic acid DOI: 10.48317/IMIST.PRSM/morjchem-v9i3.23865 -
C c single bond confidence 1.0
“Meanwhile, the peaks at around 1139 cm-1 and 726 cm-1 corresponded to C-C-O asymmetric stretching and C-O symmetric stretching, respectively.”
Can 等 - 2023 - Choline Chloride-Based Deep Eutectic Solvent-Treat DOI: 10.3390/f14030569 -
Hydroxyl (O-H) confidence 1.0
“(O-H) 434 to The FTIR spectra result showed that functional groups 2,997-3,726cm-1 (C-H) findings confirm specific wavenumber, functional These that some functional groups are exist within cm-1,(Si-H)-basedgroupsfrom2397 groupsfrom2,880to2,”
Anwar-ul-Haq 等 - 2022 - Role of Bacterial Consortium and Synthetic Surfact DOI: 10.3389/fenrg.2022.874492 -
Borate confidence 1.0
“(cm-1) LP1 475 667 - 1554 1613 1648 ∼470 Pb-O LP2 470 726 - 1506 1615 1694 bond vibrations O-B-O LP3 473 761 - 1540 1684 bond bending vibrations ∼726 B-O-B LP4 468 726 996 1506 1684 linkages bending and isolated BO3LP5 473 738 1008 1507 161”
Balachander 等 - 2013 - IR analysis of borate glasses containing three alk DOI: 10.2306/scienceasia1513-1874.2013.39.278 -
Alkyl C-H confidence 1.0
“The band at 726 (band 7) observed in the spectrum is assigned to the CH rocking mode [34].”
Assessment of Chemical and Physico-Chemical Properties of Cyanobacterial Lipids for Biodiesel Production DOI: 10.3390/md11072365 -
Acetate confidence 1.0
“cm-1 cm-1 (C=O+CCO) δ(O=C-O), plane vibration, 798 cm-1 to the group (C=O+CCO) bending and at 726 cm-1 to the group δ(O=C-O), plane vibration, 798 to the group bending and at 726 to the group (δ(C=O) and δ(CH)) of the aromatic ring [31].”
Drobota 等 - 2020 - Preparation and Characterization of Electrospun Co DOI: 10.3390/ma13183961 -
Acetate confidence 1.0
“show C-H bond stretching vibrations, whereas the peak at specifies 1,747cm-1 cm-1 C=O stretch, and 1,769 depicts CH2/ 1,726cm-1 CH3 stretch in the EVA particle sample.”
Hossain 等 - 2023 - First evidence of microplastics and their characte DOI: 10.3389/fenvs.2023.1232931
Have a spectrum with this band?
Upload your FTIR spectrum and get a full interpretation report — peak assignments with literature citations, library matches, and a literature-backed analysis — in seconds.