What absorbs at 756 cm⁻¹ in an FTIR spectrum?
A band near 756 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 756 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 | 7 | 6 | 1.0 |
| Aromatic ring | 5 | 4 | 1.0 |
| Ring structure | 4 | 3 | 1.0 |
| Metal oxygen | 3 | 3 | 1.0 |
| Amide | 2 | 2 | 1.0 |
| Hydroxyl (O-H) | 2 | 2 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Oxygen heterocycle | 1 | 1 | 1.0 |
| Carbonate | 1 | 1 | 1.0 |
| N h | 1 | 1 | 1.0 |
| Phosphate (PO4) | 1 | 1 | 1.0 |
| Metal hydroxyl | 1 | 1 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| Alkene (C=C) | 1 | 1 | 1.0 |
| Methacrylate | 1 | 1 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Carboxyl (COOH) | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| Acetate | 1 | 1 | 1.0 |
| Chlorine | 1 | 1 | 0.9 |
| Siloxane (Si-O-Si) | 1 | 0 | 1.0 |
| Silicon-oxygen (Si-O) | 1 | 0 | 1.0 |
| Silicon (Si) | 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 |
|---|---|---|---|
| Polyurethane | 756, 2270, 1700 | Alkyl C-H | 1 |
| TiO2 | 756, 1700, 1093 | Metal oxygen, Alkyl C-H | 1 |
| ZnO | 756, 1400, 3430 | Metal oxygen, Alkyl C-H | 1 |
| microplastics | 756, 1643, 1614 | 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 756 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
“Otherwise, peaks at 756 and 698 due to C-H out-of-plane bending vibration indicate that only one substituent in the benzene ring is present [38].”
Campanale 等 - 2023 - Fourier Transform Infrared Spectroscopy to Assess DOI: 10.3390/polym15040911 -
Alkyl C-H confidence 1.0
“The as-synthesized VB cm-1, related to the out-of-plan C-H bending FTIR detected a new bond at 756 vibration.”
Sensitization of ZnO nanoparticle by vitamin B12: Investigation of microstructure, FTIR and optical properties DOI: 10.1016/j.materresbull.2016.07.029 -
Ring structure confidence 1.0
“cm-1 741 (ring vibration due to 1,2-disubstituted benzene) cm-1 756 cm-1 2-HP-(cid:2)-CD, 3401 ( OH stretching) cm-1 2928 ( CH stretching) cm-1 (H O H bending) 1652 cm-1 (C H stretching) 1164”
Telmisartan complex augments solubility, dissolution and drug delivery in prostate cancer cells DOI: 10.1016/j.carbpol.2013.09.077 -
Aromatic ring confidence 1.0
“LLM confirmed rule peak-group candidate”
Ahmad 等 - 2020 - Green Synthesis and Characterization of Zinc Oxide DOI: 10.3390/biom10030425 -
Aromatic ring confidence 1.0
“Peaks seemingly due to O-H stretch appeared at 3460 cm-1, cm-1, C-H stretch (aromatic) at 2915 C=O stretch due to vinyl acetate at 1730 C=O at 1727 cm-1, 1610 cm-1, 778 cm-1, 1517 cm-1, and 756 cm-1 corresponds to crystalline form”
How to Improve Solubility and Dissolution of Irbesartan by Fabricating Ternary Solid Dispersions: Optimization and In-Vitro Characterization DOI: 10.3390/pharmaceutics14112264 -
C-O single bond confidence 1.0
“ether and tertiary alcohols were shown by the bands at 1066 and 756 cm-1, respectively The non-appearance of these unique crests in the spectral band of synthesized nanoparticles [32].”
Green Synthesis of TiO2 Nanoparticles Using Acorus calamus Leaf Extract and Evaluating Its Photocatalytic and In Vitro Antimicrobial Activity DOI: 10.3390/catal12020181 -
Alkyl C-H confidence 1.0
“detected at 2962.67 cm-1 and 756.46 cm-1 can be attributed to the C-H stretching and bending vibration, respectively.”
Cimavilla-Roman 等 - 2020 - Influence of silica aerogel particles on the foami DOI: 10.1016/j.eurpolymj.2020.109884 -
Metal hydroxyl confidence 1.0
“cm-1, near 1030 One way to differentiate between nephrite and jadeite and its bending equivalent at 470 cm-1 cm-1, is the presence of peaks near 756 and 685 Al-OH bands that can be seen near 910 in the in-plane cm-1 FTIR reference spectrum”
Delgado Robles 等 - 2015 - Non-destructive in situ spectroscopic analysis of DOI: 10.1186/s40494-015-0048-z
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