What absorbs at 2340 cm⁻¹ in an FTIR spectrum?
A band near 2340 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 2340 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 |
|---|---|---|---|
| Carbon dioxide | 8 | 7 | 1.0 |
| Alkyl C-H | 3 | 2 | 1.0 |
| Amide | 2 | 2 | 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 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Adsorbed carbon monoxide | 1 | 1 | 1.0 |
| C=n | 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 | 2340, 1400, 3430 | Alkyl C-H, Methacrylate, Amide | 1 |
| nanoparticles | 2340, 1732, 1647 | Alkyl C-H, Methacrylate, 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 2340 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
-
Adsorbed carbon monoxide confidence 1.0
“(A) Changes in the IR peak at around 2100 after switching to a flow of 2.5% O and (B) corresponding changes in the peak 2 cm-1, intensity (curve b) and intensity of the adsorbed CO peak (2340 curve a).”
In Situ Transient FTIR and XANES Studies of the Evolution of Surface Species in CO Oxidation on Au/TiO<sub>2</sub> DOI: 10.1021/jp0568733 -
Carbon dioxide confidence 1.0
“cm-1) (≈2340 some of the spectra in Figure 10 show a carbon dioxide band and artefacts Note that some of the spectra in Figure 10 show a carbon dioxide band (≈2340 cm-1) and cm-1.”
Complexation of Anthocyanin-Bound Blackcurrant Pectin and Whey Protein: Effect of pH and Heat Treatment DOI: 10.3390/molecules27134202 -
Amide confidence 1.0
“The promiin Figure 4A-C, a new peak at 2340 related to the = nent peaks in the spectrum of the original nanofibers MnO 4-C N conjugation appeared, which, together with cm-1”
Zargham 等 - 2014 - Influence of KMnO4 concentration and treatment tim DOI: 10.1515/epoly-2014-0080 -
Carbon dioxide confidence 1.0
“cm-1 1200 The band at 2340 corresponds to the appearance of carbon dioxide in 355 the thin layer as a result of the complete oxidation of glycerol molecule and the 1200 356”
The influence of stepped Pt[n(111)×(110)] electrodes towards glycerol electrooxidation: Electrochemical and FTIR studies DOI: 10.1016/j.electacta.2020.136187 -
Water (H2O) confidence 1.0
“The other peaks around 3406 cm-1,1623 cm-1 cm-1 are related to absorbed water, and 2340 and 2360 cm-1 are attributed to CO 2[28].”
A new method of synthesis well-dispersion and dense Fe3O4@SiO2 magnetic nanoparticles for DNA extraction DOI: 10.1016/j.jmmm.2017.03.025 -
Carbon dioxide confidence 1.0
“LLM confirmed rule peak-group candidate”
The influence of adsorbed substances on alkaline methanol electro-oxidation DOI: 10.1016/j.electacta.2018.10.073 -
Alkyl C-H confidence 1.0
“single ZnO and ZnO:N films, there are almost no absorption features above 3000 The IR lines at cm-1 cm-1 2960 and 2850 are assigned to C-H stretching modes, while the absorption features at cm-1 2340 are due to atmospheric CO (seen in all s”
Ivanova 等 - 2020 - Deposition and study of N-In co-doped sol-gel ZnO DOI: 10.1088/1742-6596/1492/1/012027 -
Alkyl C-H confidence 1.0
“For QU-loaded natural saponite and synthetic saponite aliphatic (C-H) band vibration are shown at 2340 cm-1 and 2949 cm-1.”
Kumaresan 等 - 2019 - Synthesis of Saponite Based Nanocomposites to Impr DOI: 10.3390/ph12030105
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