What absorbs at 2872 cm⁻¹ in an FTIR spectrum?
A band near 2872 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 2872 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 | 18 | 18 | 1.0 |
| Methyl | 6 | 6 | 1.0 |
| Methacrylate | 6 | 6 | 1.0 |
| Acetate | 6 | 6 | 1.0 |
| Methoxy (OCH3) | 5 | 5 | 1.0 |
| Carboxyl (COOH) | 4 | 4 | 1.0 |
| Ketone | 3 | 3 | 1.0 |
| Ester | 3 | 3 | 1.0 |
| Carbonyl (C=O) | 3 | 3 | 1.0 |
| Amide | 3 | 3 | 1.0 |
| C-O single bond | 2 | 2 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| N h | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Chitosan | 1 | 1 | 1.0 |
| Protein | 1 | 1 | 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 |
|---|---|---|---|
| chitosan | 2872, 1650, 1655 | Alkyl C-H, Acetate, Methacrylate | 2 |
| chitin | 2872, 1650, 1655 | Alkyl C-H, Methacrylate, Acetate | 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 2872 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
“Second, peak axial stretching of C-H is depicted at 2872 Three types of amide cm-1, cm-1 cm-1, groups of chitosan, which were identified at 1644 1569 and 1320 corresponded to C = O stretching (amide I), N-H bending (amide II), and C-N stret”
Synthesis and characterizations of o-nitrochitosan based biopolymer electrolyte for electrochemical devices DOI: 10.1371/journal.pone.0212066 -
Alkyl C-H confidence 1.0
“1722cm-1 (-CHO) absorption at and C-H stretching of aldeThe spectra incorporated not only the protein peaks at hyde (-CHO) absorption at wave number 2872.”
Sukprasert 等 - 2020 - Synchrotron FTIR Light Reveals Signal Changes of B DOI: 10.1155/2020/6149713 -
Acetate confidence 1.0
“the CH3 and CH2 stretching (CHS) peak baseline, 2999-2800 with CH3-as, CH2-as CH3-s and CH2-s peaks at 2957, 2921, 2872 cm-1,”
Implication of modified molecular structure of lipid through heat-related process to fatty acids supply in Brassica carinata seed DOI: 10.1016/j.indcrop.2014.08.025 -
Alkyl C-H confidence 1.0
“These can be briefly described as 3280 (H-O-H stretching), 2957 cm-1 cm-1 (asymmetric CH stretching), 2920 (asymmetric CH stretching), 2872 (sym-”
Bel'skaya 等 - 2021 - Application of FTIR Spectroscopy for Quantitative DOI: 10.3390/diagnostics11122391 -
Chitosan confidence 1.0
“In addition, in this study, XRD latus) and commercial chitosan showed bands at 2872 and”
Characteristics of cricket (Gryllus bimaculatus) chitosan and chitosan-based nanoparticles DOI: 10.1007/s10068-018-0314-4 -
Alkyl C-H confidence 1.0
“The Analysis of the Surface Chemical Structure of Corona BOPP Film As shown in Figure 1, Sample a represents pristine BOPP film and the absorption peaks at 2950 cm-1 and 2872 correspond to the absorption peaks of methyl symmetric and asymme”
Ding 等 - 2020 - Study on the Behavior of BOPP Film Treated by Coro DOI: 10.3390/coatings10121195 -
Alkyl C-H confidence 1.0
“LLM confirmed rule peak-group candidate”
Preformulation Studies of Ezetimibe-Simvastatin Solid Dispersions in the Development of Fixed-Dose Combinations DOI: 10.3390/pharmaceutics14050912 -
Hydroxyl (O-H) confidence 1.0
“Whereas the FTIR spectrum of SIM showed main absorption bands, significant to free O-H stretching vibration at 3547 cm-1, aliphatic C-H vibrations at 2951 cm-1, 2930 cm-1, 2872 cm-1, and”
Screening of Fenofibrate-Simvastatin Solid Dispersions in the Development of Fixed-Dose Formulations for the Treatment of Lipid Disorders DOI: 10.3390/pharmaceutics15020603
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