What absorbs at 1728 cm⁻¹ in an FTIR spectrum?
A band near 1728 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 1728 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 |
|---|---|---|---|
| Carbonyl (C=O) | 38 | 31 | 1.0 |
| Ester | 26 | 23 | 1.0 |
| Carboxyl (COOH) | 23 | 22 | 1.0 |
| Acetate | 22 | 21 | 1.0 |
| Methacrylate | 21 | 20 | 1.0 |
| Amide | 20 | 19 | 1.0 |
| Ketone | 18 | 17 | 1.0 |
| Methoxy (OCH3) | 5 | 5 | 1.0 |
| C-O single bond | 5 | 5 | 1.0 |
| Carbohydrate | 3 | 3 | 1.0 |
| Alkene (C=C) | 3 | 3 | 1.0 |
| Alkyl C-H | 3 | 3 | 1.0 |
| Acetyl | 3 | 2 | 1.0 |
| Urethane | 2 | 2 | 1.0 |
| Aromatic ring | 2 | 2 | 1.0 |
| Silicon-oxygen (Si-O) | 2 | 2 | 1.0 |
| Silicon (Si) | 2 | 2 | 1.0 |
| N h | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Quinone | 1 | 1 | 1.0 |
| Chlorine | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| Metal oxygen | 1 | 0 | 1.0 |
| Phospholipid | 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 |
|---|---|---|---|
| chitosan | 1728, 1650, 1655 | Acetate | 1 |
| Cellulose | 1728, 1735, 1650 | Acetate | 1 |
| lignin | 1728, 1035, 1510 | 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 1728 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
-
Acetate confidence 1.0
“Besides, cm-1 a band observed at 1728 in the spectrum of UT-EFB was due to C=O stretching but this peak was disappeared”
Hassan 和 Badri - 2014 - Lignin Recovery from Alkaline Hydrolysis and Glyce DOI: 10.1063/1.4895236 -
Acetyl confidence 1.0
“The new peaks at 1728 was attributed to the increasing of amorphous region of modified EFB the functional group stretching the acetyl group C=O”
Jahi 等 - 2020 - Empty Fruit Bunch Cellulose based Sorbent for Oil DOI: 10.17576/jsm-2020-4909-29 -
Acetate confidence 1.0
“5 Effect of percentage grafting on acid resistance behaviour cm-1 FTIR analysis which is due to the stretching shows a peak at 2992 cm-1 vibrations of C-H and a strong band at 1728 which is attributed to C=O (carbonyl group of esters stretc”
Graft copolymerization of methyl methacrylate on Meizotropis Pellita fibres and their applications in oil absorbency DOI: 10.1007/s13726-020-00869-7 -
Water (H2O) confidence 1.0
“The five vibrational features occur at 1030 cm1 (Si-F in gas phase SiF4), 1076 cm1 (Si-O in SiO2 film), 1728 cm1 (H2O scissors mode of adsorbed water), 3482 cm1 (O-H stretch of adsorbed H2O), and 3642 (SiO-H in surface silanol groups or H-X”
Montano-Miranda 和 Muscat - 2003 - Gas-phase HFvapor etching of thermal silicon diox DOI: 10.4028/www.scientific.net/SSP.92.207 -
Alkyl C-H confidence 1.0
“Figure 3 aldehyde-acetal The interconversion was followed by the cm-1 C-H disappearance of the carbonyl peak at 1728 and the cm-1.”
Razgon 等 - 2008 - Ozonolysis-based route to the in situ formation of DOI: 10.1021/la703120c -
Acetate confidence 1.0
“At room temperature, the intensity ratio of the band at 1728 (assigned to the C-O stretching mode) and the band at 1147 (assigned to the stretching modes of the tert-butoxy group) in the external reflection infrared spectrum of the LB film”
Shin 等 - 2002 - Structural comparison of Langmuir-Blodgett and spi DOI: 10.1021/la020135d -
Carboxyl (COOH) confidence 1.0
“The peak at 1728 represents the carboxylic acids and ketones symmetrical Where, Y is the response predicted, X and X are the indei j”
Bio-sorption of a bi-solute system of copper and lead ions onto banana peels: characterization and optimization DOI: 10.1007/s40201-021-00632-x -
Amide confidence 1.0
“In parallel with the cm-1 to the free carboxyl groups after the modification of -NH2 CS groups with succinic anhydride, while previous data, CS-Succ displays a new peak at 1728 matching to the free carboxyl groups after the successful modif”
Microencapsulation of Fluticasone Propionate and Salmeterol Xinafoate in Modified Chitosan Microparticles for Release Optimization DOI: 10.3390/molecules25173888
Have a spectrum with this band?
Upload your FTIR spectrum and get a full interpretation report — peak assignments with literature citations, library matches, and a literature-backed analysis — in seconds.