What absorbs at 1721 cm⁻¹ in an FTIR spectrum?
A band near 1721 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
Possible functional-group assignments
| Functional group | Supporting facts | Cited sources | Top confidence |
|---|---|---|---|
| Carbonyl (C=O) | 10 | 10 | 1.0 |
| Carboxyl (COOH) | 4 | 3 | 1.0 |
| Ester | 2 | 1 | 0.95 |
| C-O single bond | 1 | 1 | 0.9 |
| Imide | 1 | 0 | 0.9 |
Ranking reflects accumulated literature evidence, not a single authoritative rule. Always confirm against your sample context.
Literature behind these assignments
-
Carboxyl (COOH) confidence 1.0
“Explicit assignment in text.”
Olanipekun 等 - 2014 - Adsorption of lead over graphite oxide DOI: 10.1016/j.saa. -
Carbonyl (C=O) confidence 1.0
“Explicit assignment in text”
Tyubaeva 等 - 2023 - Development of Nonwoven Fibrous Materials Based on DOI: 10.3390/polym15153167 -
Ester confidence 0.95
“Explicit assignment in text: '1721 for the carbonyl (C=O) stretching of the ester group'”
Duangsri 等 - 2020 - Enhanced polyhydroxybutyrate (PHB) accumulation in DOI: 10.1007/s10811-020-02272-4 -
Carboxyl (COOH) confidence 0.95
“New peak assigned to carboxyl group formation.”
Makhliyo 等 - 2023 - Preparation of oxidized nanocellulose by using pot DOI: 10.21203/rs.3.rs-2033622/v1 -
Carbonyl (C=O) confidence 0.9
“Text: 'Fourier transfer infrared peak at 1721 cm-1, corresponding to the carbonyl stretching of a fluorenone moiety'”
Noh 等 - 2005 - Keto defect sites in fluorene-based organic field- DOI: 10.1063/1.1897068 -
Carbonyl (C=O) confidence 0.9
“Explicit assignment in text”
Abd Rahman 等 - 2014 - UV-Curable Acrylated Coating From Epoxidized Palm DOI: 10.1063/1.4895237 -
Carbonyl (C=O) confidence 0.9
“Text: 'C=O stretching at 1721 cm-1, C-O-C stretching C-C and C-O stretching at 1721'”
Cetmi 等 - 2019 - Preparation of electrospun polycaprolactone nanofi DOI: 10.1002/elsc.201900009 -
Carbonyl (C=O) confidence 0.9
“Stretching vibration of C=O bond at 1721 cm-1.”
Deng 等 - 2019 - New Insights into the Interaction between Graphene DOI: 10.3390/nano9101429
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