What absorbs at 1340 cm⁻¹ in an FTIR spectrum?
A band near 1340 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 1340 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 | 12 | 11 | 1.0 |
| Amide | 10 | 10 | 1.0 |
| Secondary amine | 6 | 6 | 1.0 |
| C n single bond | 6 | 6 | 1.0 |
| Protein | 5 | 5 | 1.0 |
| Aromatic ring | 4 | 4 | 1.0 |
| Carboxyl (COOH) | 4 | 4 | 1.0 |
| Methacrylate | 4 | 4 | 1.0 |
| Acetate | 4 | 4 | 1.0 |
| C c single bond | 3 | 3 | 1.0 |
| Hydroxyl (O-H) | 3 | 3 | 1.0 |
| Methoxy (OCH3) | 3 | 3 | 1.0 |
| C-O single bond | 3 | 3 | 1.0 |
| N-O bond | 2 | 2 | 1.0 |
| Carbonate | 2 | 2 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| Carbon dioxide | 1 | 1 | 1.0 |
| Nitro (NO2) | 1 | 1 | 1.0 |
| Borate | 1 | 1 | 1.0 |
| N h | 1 | 1 | 1.0 |
| Siloxane (Si-O-Si) | 1 | 1 | 1.0 |
| Silicon-oxygen (Si-O) | 1 | 1 | 1.0 |
| Sulfonate | 1 | 1 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| Fluorine (C-F) | 1 | 1 | 0.9 |
| N eq o | 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 |
|---|---|---|---|
| SiO2 | 1340, 1739, 699 | Alkyl C-H | 1 |
| ZnO | 1340, 1400, 3430 | Alkyl C-H, Amide | 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 1340 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
-
Carbonate confidence 1.0
“COOcm-1) (Figure 6B), an initial section corresponding to (1636 and 1599 is observed, cm-1 cm-1, followed by a peak at 1340 and 1457 indicative of the presence of CO 3, and a cm-1, peak at 1033 corresponding to the presence of PO groups.”
Remineralization Potential of Three Restorative Glass Ionomer Cements: An In Vitro Study DOI: 10.3390/jcm12062434 -
Amide confidence 1.0
“N=O (NO ) symmetric stretching 1340 2 C-N stretching (aryl) 1180 In plane aromatic C-H deformation”
Synthesis and characterization of Heck-cross coupling 4-(4-nitrostyryl) aniline as potential precursor in Schiff-base synthesis DOI: 10.1063/1.5002293 -
Alkyl C-H confidence 1.0
“The sharp peak at 1340 is attributed to the C-H bending in alkanes and the 1097”
Krishnan 等 - 2020 - Leaf Extract ofDillenia indicaas a Source of Selen DOI: 10.3390/coatings10070626 -
N-O bond confidence 1.0
“the TNT NO bands (1340 and 1546 It is clear from the spectra shown that the peaks intensity of these bands 2 decrease when the concentrations decrease.”
Primera-Pedrozo 等 - 2007 - Detection of 2,4,6-trinitrotoluene on non traditio DOI: 10.1117/12.720405 -
Acetate confidence 1.0
“It shows six major diffraction peaks at cm-1 cm-1 and 1406 corresponds to the band at 1340 31.51, 34.33, 35.98, 47.49, 56.29 and 62.59, which C=O bending vibrations and C=O stretching can be assigned to diffraction from (100), (002),”
Saini 等 - 2013 - Structural and Optical Properties of ZnO Nanoparti DOI: 10.1063/1.4810170 -
Acetate confidence 1.0
“But more broadening is noticed in case cm(cid:3)1) due to its high dielectric of C-O-C stretching (1340 of polymer electrolytes containing PC along with the disconstant as compared to DEC.”
Influence of high and low dielectric constant plasticizers on the ion transport properties of PEO: NH4HF2 polymer electrolytes DOI: 10.1177/0954008319894043 -
Sulfonate confidence 1.0
“It may also be observed that a broadened peak around 1340 cm-1 is present is present in the salt samples which can be attributed to the interactions of the sulfonate in the salt samples which can be a(cid:6)ributed to the interactions of th”
Anis 等 - 2023 - Studies on Polybenzimidazole and Methanesulfonate DOI: 10.3390/polym15132821 -
confidence 1.0
“cm-1 cm-1 cm-1 C-H bending), 910 (silane group), 1070 (Si-O-Si asymmetric stretching), 1340 (aromatic Ccm-1 cm-1 cm-1 (CO2+”
Bahramnia 等 - 2022 - The Effect of 3-(Glycidoloxy Propyl) Trimethoxy Si DOI: 10.21203/rs.3.rs-381518/v1
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