What absorbs at 749 cm⁻¹ in an FTIR spectrum?
A band near 749 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 6 cited sources
Quick answer
A band near 749 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 | 3 | 3 | 1.0 |
| Aromatic ring | 2 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Nitrogen heterocycle | 1 | 1 | 1.0 |
| Metal oxygen | 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 |
| Oxalate | 1 | 0 | 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 |
|---|---|---|---|
| ZnO | 749, 1400, 3430 | Alkyl C-H | 2 |
| ZIF-8 | 749, 1747, 1145 | Alkyl C-H, Ring structure | 1 |
| ZnO nanoparticles | 749, 1219, 1726 | 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 749 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
-
Hydroxyl (O-H) confidence 1.0
“753 (2005) 749cm-1 [15] S.Naghibi,H.R.MadaahHosseini,M.A.FaghihiSani,Colloidalstabilityofdextran at and the hydroxyl stretching vibrations were inand dextran/poly ethylene glycol coated TiO2 nanoparticles by hydrothermal astensified.”
Gharagozlou 和 Naghibi - 2018 - Sensitization of ZnO nanoparticles by metal-free p DOI: 10.1016/j.jlumin.2017.12.020 -
confidence 1.0
“749cm-1 The bands located near is due to Sb doping, films The produced ZnO were evaluated for surface morwhereas Al and Sb codopant band is located near the 816cm-1 Cm-1 phology using a FESEM (JEOL-JSM 6100), as shown in [33].”
Verma 等 - 2022 - Morphological, Structural, and Optical Properties DOI: 10.1155/2022/6250706 -
Alkyl C-H confidence 1.0
“The bands at 1267 cm-1 and 749 cm-1 are attributed to C-H and C-N deformation, respectively [45].”
Regularities of Encapsulation of Tolfenamic Acid and Some Other Non-Steroidal Anti-Inflammatory Drugs in Metal-Organic Framework Based on -Cyclodextrin DOI: 10.3390/pharmaceutics15010071 -
Metal oxygen confidence 1.0
“However, the Al-O stretching vibration consistent with the flotation test results, which further proves cm-1 peak at 749 does not show obvious band shift, which”
Man 等 - 2019 - Flotation Separation of Diaspore and Kaolinite by DOI: 10.3389/fchem.2019.00813 -
Nitrogen heterocycle confidence 1.0
“vibration of the imidazole ring appeared at 3131 ing to MCG plates, as well as peaks corresponding to ZIF-67 (at ~670 and 749 cm-1) and a”
XRD and Spectroscopic Investigations of ZIF—Microchannel Glass Plates Composites DOI: 10.3390/ma16062410 -
Alkyl C-H confidence 1.0
“The spectrum at 970 cm-1 is allocated to =C-H out-of-plane bending vibration from aromatics, and the characteristic band at 749 is attributed to C-H vibration in benzene.”
Nanoliposomes containing three essential oils from the Artemisia genus as effective larvicides against Aedes aegypti and Anopheles stephensi DOI: 10.1038/s41598-023-38284-6
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