What absorbs at 1125 cm⁻¹ in an FTIR spectrum?
A band near 1125 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 1125 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 |
|---|---|---|---|
| C-O single bond | 7 | 7 | 1.0 |
| Methoxy (OCH3) | 6 | 6 | 1.0 |
| Methacrylate | 6 | 6 | 1.0 |
| Acetate | 6 | 6 | 1.0 |
| Phosphate (PO4) | 4 | 4 | 1.0 |
| Metal oxygen | 4 | 4 | 1.0 |
| Alkyl C-H | 4 | 4 | 1.0 |
| Silicon-oxygen (Si-O) | 4 | 4 | 1.0 |
| Nucleic acid | 4 | 4 | 1.0 |
| Hydroxyl (O-H) | 3 | 3 | 1.0 |
| Silicon (Si) | 3 | 3 | 1.0 |
| Secondary amine | 3 | 2 | 1.0 |
| C n single bond | 3 | 2 | 1.0 |
| Amide | 3 | 2 | 1.0 |
| Carbohydrate | 2 | 2 | 1.0 |
| C-S single bond | 1 | 1 | 1.0 |
| Carboxyl (COOH) | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Siloxane (Si-O-Si) | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 0.9 |
| Methyl | 1 | 1 | 0.8 |
| C=n | 1 | 0 | 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 |
|---|---|---|---|
| saliva | 1125, 1648, 1664 | Methacrylate, Acetate, Methoxy (OCH3) | 1 |
| lignin | 1125, 1035, 1510 | Methacrylate, Acetate, C-O single bond | 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 1125 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
-
Nucleic acid confidence 1.0
“The analysis in Figure 3a,b shows that in the transformation from B-DNA to Z-DNA, cm-1 cm-1 the characteristic peaks at ~1125 and ~925 appeared, which are attributed to cm-1 Z-DNA.”
Assessing B-Z DNA Transitions in Solutions via Infrared Spectroscopy DOI: 10.3390/biom13060964 -
Alkyl C-H confidence 1.0
“cm-1 C-O 1214-1221 [6, 27] G2 1213 x x x x x (x) x stretch of guaiacyl ring: cm-1 C-H 1140-1145 [6, 27, 28] G3 1151 x x x (x) Possibly stretch of guaiacyl ring: cm-1 C-H [6] G4 1124 x x x (x) x (x) Aromatic deformation of guaiacyl ring: 112”
Characterisation of Authentic Lignin Biorefinery Samples by Fourier Transform Infrared Spectroscopy and Determination of the Chemical Formula for Lignin DOI: 10.1007/s12155-017-9861-4 -
confidence 1.0
“The previous discusfilms were treated by H this peak to each vibration, we assign the peak at 1125 sion suggests that the thickness difference in the SiO 2 cm-1 Si-O as the combined contribution of the vibration of layer (cf.”
Lu 和 Mi - 2005 - Characterization of the interfacial interaction be DOI: 10.1021/ma0486896 -
Amide confidence 1.0
“cm(cid:0) cm(cid:0) 1 1 After the attachment of polyaniline a band at 1288 After chromium adsorption in the case of PANIDSC@Cr three peaks and 1125 25◦, 28.2◦, 40.4◦ = 2θ C-N were observed at in the case of PANIDSC, PANIDSC@Cr is the charac”
Efficient removal of Cr(VI) by polyaniline modified biochar from date (Phoenix dactylifera) seed DOI: 10.1016/j.gsd.2021.100653 -
Phosphate (PO4) confidence 1.0
“The peak at 1125 can be assigned to either the stretching 3 3-2 vibration of P-O-Si (25), asymmetric vibration of PO (42, 46) or an overlap of both peaks.”
Al-Sallami 等 - 2019 - Reactivity of oil-soluble IL with silicon surface DOI: 10.1002/ls.1456 -
Acetate confidence 1.0
“The C-O stretch cm-1 absorption peak at 1125 for NMA expressed a similar trend to shift to lower wavenumbers for both 2ET and DGME, indicating that new X-Y interactions were formed [25].”
The development of powder injection moulding binders: A quantification of individual components' interactions DOI: 10.1016/j.powtec.2015.07.046 -
Acetate confidence 1.0
“phosphodiester groups from phosphorylated molecules (1125 and 1076 and C-O stretching vibration coupled with C-O bending of the C-OH groups of carbohydrates cm-1.”
The Role of the Preanalytical Step for Human Saliva Analysis via Vibrational Spectroscopy DOI: 10.3390/metabo13030393 -
Nucleic acid confidence 1.0
“cm-1) cm-1 (±7 RNA-specific infrared absorptions at 1125 and 984 [43] are particular peaks considered diagnostic of the contribution of RNA in the nucleic acid backbone vibrations [43-45].”
Synchrotron-Based Fourier-Transform Infrared Micro- Spectroscopy of Cerebrospinal Fluid from Amyotrophic Lateral Sclerosis Patients Reveals a Unique Biomolecular Profile DOI: 10.3390/cells12111451
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