What absorbs at 720 cm⁻¹ in an FTIR spectrum?
A band near 720 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 720 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 | 27 | 26 | 1.0 |
| Metal oxygen | 6 | 6 | 1.0 |
| Methoxy (OCH3) | 4 | 4 | 1.0 |
| Methacrylate | 4 | 4 | 1.0 |
| C-O single bond | 4 | 4 | 1.0 |
| Acetate | 4 | 4 | 1.0 |
| Chlorine | 3 | 3 | 1.0 |
| Secondary amine | 3 | 3 | 1.0 |
| C-S single bond | 3 | 3 | 1.0 |
| Ring structure | 3 | 3 | 1.0 |
| Alkene (C=C) | 3 | 3 | 1.0 |
| Carbonate | 3 | 3 | 1.0 |
| Silicon-oxygen (Si-O) | 3 | 2 | 1.0 |
| C n single bond | 2 | 2 | 1.0 |
| Amide | 2 | 2 | 1.0 |
| Hydroxyl (O-H) | 2 | 2 | 1.0 |
| Aromatic ring | 2 | 2 | 1.0 |
| C c single bond | 2 | 2 | 1.0 |
| Fatty acid | 2 | 2 | 1.0 |
| Hydrogen bond | 2 | 2 | 1.0 |
| Imide | 1 | 1 | 1.0 |
| Chitosan | 1 | 1 | 1.0 |
| Silicate | 1 | 1 | 1.0 |
| Lipid | 1 | 1 | 1.0 |
| Borate | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| N-O bond | 1 | 1 | 1.0 |
| Siloxane (Si-O-Si) | 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 |
|---|---|---|---|
| LDPE | 720, 1720, 1737 | Alkyl C-H, Methacrylate, Methoxy (OCH3) | 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 720 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
“FTIR results showed cm-1, the stretching vibrations of Si-O at 720 asymmetric stretching vibrations of Si-O-Si cm-1.”
Mimosa pudica mediated praseodymium substituted calcium silicate nanostructures for white LED application DOI: 10.1016/j.jallcom.2016.08.064 -
Metal oxygen confidence 1.0
“LLM confirmed rule peak-group candidate”
Cu2+–Mn2+-Co-doped CdO nanocrystallites: comprehensive research on phase, morphology and optoelectronic properties DOI: 10.1007/s11164-020-04202-y -
Hydrogen bond confidence 1.0
“In addition, a 720 cm-1 peak, which is one of the PCM char- (2) the hydrogen bonding between the paraffin and the lignin, cellulose, and hemicellulose”
n-Heptadecane-Impregnated Wood as a Potential Material for Energy-Saving Buildings DOI: 10.3390/f13122137 -
N-O bond confidence 1.0
“Since FA enter the amylose double helix and form cm-1 hydrogen bonds with starch molecules, no absorption peak of FA at 720 was observed hydrogen bonds with starch molecules, no absorption peak of FA at 720 cm-1 was obcm-1 in the complexes”
Formation of Intermediate Amylose Rice Starch–Lipid Complex Assisted by Ultrasonication DOI: 10.3390/foods11162430 -
Alkene (C=C) confidence 1.0
“Index (DBI) and Terminal Double Bond Index (TDBI) were cm-1 cm-1 calculatedtoevaluatefunctionalbondformationandLDPEchain Peaks at 720 and near 1450 were formed due to”
Biodegradation of Unpretreated Low-Density Polyethylene (LDPE) by Stenotrophomonas sp. and Achromobacter sp., Isolated From Waste Dumpsite and Drilling Fluid DOI: 10.3389/fmicb.2020.603210 -
Alkyl C-H confidence 1.0
“The peak near 720.45 was assigned to overlap of methylene ((cid:0) Noir' Adriatic',”
Fig seeds: Combined approach of lipochemical assessment using gas chromatography and FTIR-ATR spectroscopy using chemometrics DOI: 10.1016/j.vibspec.2021.103251 -
Acetate confidence 1.0
“[63-65] Methyl-carbon stretching [66] 1102 δ(C-O) Stretching vibration (polypeptides) 720 δ(COH), δ(CCH), δ(OCH) Stretching vibration”
Hssaini 等 - 2022 - Do Pollination and Pollen Sources Affect Fig Seed DOI: 10.1155/2022/3969165 -
confidence 1.0
“The peaks at 712.6eV and satellite peaks at 719.5eV correspond to Fe 2p3/2, the peaks at 726.04eV correspond Fig.”
Structural and magnetic properties of Gd-Zn substituted M-type Ba-Sr hexaferrites by sol-gel auto-combustion method DOI: 10.1016/j.jallcom.2019.06.348
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