What absorbs at 723 cm⁻¹ in an FTIR spectrum?
A band near 723 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 723 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 | 13 | 13 | 1.0 |
| Hydroxyl (O-H) | 2 | 2 | 1.0 |
| N h | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Metal oxygen | 1 | 1 | 1.0 |
| Lipid | 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 |
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 |
|---|---|---|---|
| polypropylene | 723, 1030, 1600 | Alkyl C-H, Hydroxyl (O-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 723 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
“cm-1 vibrations CH and CH bands were clearly seen in the region of 1465 while the band at 723 2 3 was assigned to a CH [25,26].”
Monitoring Enzymatic Hydroesterification of Low-Cost Feedstocks by Fourier Transform InfraRed Spectroscopy DOI: 10.3390/catal9060535 -
Hydroxyl (O-H) confidence 1.0
“Sample S076 consists only of trans-vacant (tv) layers because its DTG curve and IR spectrum contain cm-1, a single dehydroxylation maximum at T = 723 °C and an OH stretching band 3675 respectively.”
Drits 等 - 2011 - New insight into the structural transformation of DOI: 10.2138/am.2011.3605 -
Acetate confidence 1.0
“gion includes shoulder peak at 1,238 and a sharp peak at 1,157 representing stretching vibration of C-O ester groups and peak at cm-1 723 associated with out-of-plane vibration of cis -HC=CHgroup”
Chemical, thermal, rheological and FTIR studies of vegetable oils and their effect on eggless muffin characteristics DOI: 10.1111/jfpp.13978 -
Alkyl C-H confidence 1.0
“cm-1 cm-1, 1656 are vibrating peaks of cis (C=C) and cis (C-H) AND and CDB have spectral similarities at 723 cm-1 groups of USFA acids.”
Martins 等 - 2019 - Approach by Raman and infrared spectroscopy in thr DOI: 10.31349/RevMexFis.65.328 -
Alkyl C-H confidence 1.0
“FTIR spectrum cm-1 (C-H) common for these types of compounds, and belong to also shows absorption bands at 723 for group the methylene carbon atoms of MEOA and HYOOA vibration.”
Salimon 等 - 2013 - Synthesis and optimization ring opening of monoepo DOI: 10.1186/2193-1801-2-429 -
Alkyl C-H confidence 1.0
“inner layer had the highest peak for the C-H bond, with bands at 723 and 2823 The symmetry deformation of CH on aliphatic hydrocarbons was assigned to the peak 3”
Physical and Chemical Characteristics of Agricultural-Plastic Wastes for Feasibility of Solid Fuel Briquette Production DOI: 10.3390/su142315751 -
Alkyl C-H confidence 1.0
“In addition, lower absorption with limited variations was cm-1 observed in absorption between 1460 and 400 (Figure 3), with a rather distinct one cm-1, cis in the band of 723 that responds to (C-H) out-of-plane deformation [27,28].”
Banou 等 - 2023 - Oil Media on Paper Investigating the Interaction DOI: 10.3390/polym15112567 -
Alkyl C-H confidence 1.0
“The peaks at 1375, 1467, and 1439 were assigned to symmetric and asymmetric vibrations of methyl groups and the peak at cm-1 723 was ascribed to rocking vibration and deformation vibration of the -CH”
Effects of processing conditions on the properties of paraffin/melamine-urea-formaldehyde microcapsules prepared by in situ polymerization DOI: 10.1016/j.rser.2017.10.002.
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