What absorbs at 719 cm⁻¹ in an FTIR spectrum?
A band near 719 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 719 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 | 11 | 10 | 1.0 |
| Aromatic ring | 2 | 2 | 1.0 |
| Fatty acid | 2 | 2 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Secondary amine | 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 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Carbonate | 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 |
|---|---|---|---|
| LDPE | 719, 1720, 1737 | Alkyl C-H, Aromatic ring | 2 |
| HDPE | 719, 1369, 1216 | Alkyl C-H, Aromatic ring | 2 |
| microplastics | 719, 1643, 1614 | Alkyl C-H, Aromatic ring | 1 |
| asphalt | 719, 1600, 1376 | Alkyl C-H, Aromatic ring | 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 719 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
“In particular, for PE at 710 and 719 cm-1 (-CH2 rocking deformation), 2847 and 2915 cm-1 (- symmetric and asymmetric stretching), 1462 and 1472 cm-1 (-CH=CHstretching) CH2 [36].”
Campanale 等 - 2023 - Fourier Transform Infrared Spectroscopy to Assess DOI: 10.3390/polym15040911 -
Alkyl C-H confidence 1.0
“The peak at 3005 attributes to the stretching vibrations of C-H in cm-1 H-C=C and the peak at 718.8 corresponds to out-of-plane bending vibrations of ACCEPTED”
Liang 等 - 2017 - Thermo-stability and aging performance of modified DOI: 10.1016/j.matdes.2017.04.060 -
Alkyl C-H confidence 1.0
“1356cm(cid:1)1 1468 and correspond to scissoring vibration of the 729cm1 methylene group, while weak peaks at 719 and can be ascribed to rocking vibration of methylene group.”
Olajire 和 Mohammed - 2020 - Green synthesis of nickel oxide nanoparticles and DOI: 10.1016/j.apt.2019.10.012 -
Alkyl C-H confidence 1.0
“The peaks at 719 cm-1 can be assigned to both CH2 rocking cm-1”
Walnut Oil Oleogels as Milk Fat Replacing System for Commercially Available Chocolate Butter DOI: 10.3390/gels8100613 -
Alkyl C-H confidence 1.0
“FTIR bands at 719 is associated with CH rocking 2 The results of measured total birefringence and the one mode of amorphous trans sequences of four or more cmK1 calculated from the crystalline axes orientation factors sequences, 1303 to CH”
Biaxial orientation in HDPE films : Comparison of infrared spectroscopy, X-ray pole figures and birefringence techniques DOI: 10.1016/j.polymer.2005.03.002 -
Alkyl C-H confidence 1.0
“719.71cm-1 to and to beeswax combination increased with increasing amounts of 718.71cm-1 which corresponds to C-H (CH 2), C-H (CH 3) beeswax, which is as expected due to the hardening effect of -C�O stretching vibrations, stretching vibrati”
Bartels 等 - 2021 - Formulation of Suppositories of Alum Produced from DOI: 10.1155/2021/6667562 -
Hydroxyl (O-H) confidence 1.0
“cm-1 (Figure 7C), 2847 (-CH symmetric stretching) (Figure 7C), 1462 (-CH bending cm-1 cm-1 deformation) (Figure 7E), 1375 (-O-H stretching), and 719 (rocking vibrational mode of -CH 2) (Figure 7G).”
Gong 等 - 2023 - Biodegradation of Low Density Polyethylene by the DOI: 10.3390/jof9060605 -
Alkyl C-H confidence 1.0
“The production and packaging of LDPE, the peak wavelength at represents the CH bend, 3 730cm-1, 719cm-1 717cm-1”
Hossain 等 - 2023 - First evidence of microplastics and their characte DOI: 10.3389/fenvs.2023.1232931
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