What absorbs at 1403 cm⁻¹ in an FTIR spectrum?
A band near 1403 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 1403 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 |
|---|---|---|---|
| Methacrylate | 5 | 5 | 1.0 |
| Acetate | 5 | 5 | 1.0 |
| Amide | 5 | 5 | 1.0 |
| Carboxyl (COOH) | 5 | 5 | 1.0 |
| Alkyl C-H | 5 | 4 | 1.0 |
| Methoxy (OCH3) | 4 | 4 | 1.0 |
| C-O single bond | 3 | 3 | 1.0 |
| Hydroxyl (O-H) | 3 | 3 | 1.0 |
| N h | 2 | 2 | 1.0 |
| Methyl | 2 | 2 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| Fatty acid | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Phosphate (PO4) | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| Carbonate | 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 |
|---|---|---|---|
| PET | 1403, 1408, 800 | Methacrylate, Acetate, Amide | 1 |
| collagen | 1403, 1408, 1660 | Amide, Methacrylate, Acetate | 1 |
| saliva | 1403, 1648, 1664 | Amide, 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 1403 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
-
Aromatic ring confidence 1.0
“Moreover, the presence of C-C stretching vibration, C-C tangential vibration and C-H out-of-plane cm-1, cm-1 bending vibration of aromatic rings are determined by the characteristic peaks at 1402.77 1459.57 and cm-1 cm-1”
Tan 等 - 2018 - Synthesis and Characterization of Polybenzoxazine DOI: 10.1063/1.5066866 -
Hydroxyl (O-H) confidence 1.0
“The wide peaks at 3425 cm-1 cm-1 β-unsaturated ketone, while the peak at 1403 indicated O-H bending of the carboxylic”
The Antifungal Properties of Tamarix aphylla Extract against Some Plant Pathogenic Fungi DOI: 10.3390/microorganisms11010127 -
Phosphate (PO4) confidence 1.0
“COO-stretch,C-Hbend 1456 1446 Lipids COO-stretch,C-Hbend 1403 1386 Lipids PO4-stretch 1236 1232 NucleicAcids”
ATR-FTIR spectroscopy as adjunct method to the microscopic examination of hematoxylin and eosin-stained tissues in diagnosing lung cancer DOI: 10.1371/journal.pone.0233626 -
Acetate confidence 1.0
“cm-1 cm-1 and 1300 (including the peak at band centered at 1076 corresponding to the cm-1 vibrational mode of skeletal cis conformation of DNA), 1403 band of symmetric CH 3 bending modes of protein methyl groups and symmetric CH bending of”
Unlocking the Diagnostic Potential of Saliva: A Comprehensive Review of Infrared Spectroscopy and Its Applications in Salivary Analysis DOI: 10.3390/jpm13060907 -
Alkyl C-H confidence 1.0
“The FTIR-ATR spectrum from Figure 2b shows the characteristic vibration of C-fibers at 1451, The FTIR-ATR spectrum from Figure 2b shows the characteristic vibration of C-fibers at 1451, The FTIR-ATR spectrum from Figure 2b shows the charact”
Drobota 等 - 2020 - Preparation and Characterization of Electrospun Co DOI: 10.3390/ma13183961 -
Carboxyl (COOH) confidence 1.0
“After the interaction with NaOL, the antisymmetric stretching peak of -C-H appeared at 2924.71 cm-1 and the peaks that appeared at 1637.26 cm-1 and 1403.19 cm-1 were contributed by the vibration -COO-, indicating that the chemical adsorptio”
Lu 等 - 2020 - Effect of manganese ions addition orders on the fl DOI: 10.37190/ppmp/126421 -
Amide confidence 1.0
“6of20 of samples derived from P5 and P6 exhibit similar spectral characteristics for both sides of the parchment, while the spectra of samples obtained from P1-P4 are dominated by an cm-1 intense absorption band at 1403 on the hair side, su”
Spectral Features Differentiate Aging-Induced Changes in Parchment—A Combined Approach of UV/VIS, -ATR/FTIR and -Raman Spectroscopy with Multivariate Data Analysis DOI: 10.3390/molecules28124584 -
Acetate confidence 1.0
“-C=Ostretches 1403.10 6.19 Sp3C-Hbend 1313.08 C-O”
The Using of Nanoparticles of Microalgae in Remediation of Toxic Dye from Industrial Wastewater: Kinetic and Isotherm Studies DOI: 10.3390/ma15113922
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