What absorbs at 1404 cm⁻¹ in an FTIR spectrum?
A band near 1404 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 1404 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 |
|---|---|---|---|
| Carboxyl (COOH) | 7 | 7 | 1.0 |
| Alkyl C-H | 5 | 5 | 1.0 |
| Amide | 5 | 4 | 1.0 |
| N h | 4 | 3 | 1.0 |
| Methoxy (OCH3) | 3 | 3 | 1.0 |
| Methacrylate | 3 | 3 | 1.0 |
| Acetate | 3 | 3 | 1.0 |
| Hydroxyl (O-H) | 2 | 2 | 1.0 |
| Protein | 2 | 2 | 1.0 |
| C-O single bond | 2 | 2 | 1.0 |
| Carbonyl (C=O) | 2 | 2 | 1.0 |
| Secondary amine | 2 | 1 | 1.0 |
| N n bond | 1 | 1 | 1.0 |
| Lipid | 1 | 1 | 1.0 |
| Amino acid | 1 | 1 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| Methyl | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| Alkene (C=C) | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Nitrogen heterocycle | 1 | 1 | 1.0 |
| Phosphate (PO4) | 1 | 1 | 0.95 |
| Carbonate | 1 | 1 | 0.9 |
| Aromatic ring | 1 | 0 | 1.0 |
| Boron nitrogen | 1 | 0 | 1.0 |
Ranking reflects accumulated literature evidence, not a single fixed rule. Always confirm against your sample context.
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 1404 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
-
Carboxyl (COOH) confidence 1.0
“Small Figure 4 shows the effect of EDTA concentration of the carboxylate bands that were observed in the EDTAand medium on the suppression of the band intensity of the cm-1 EGTA-supplemented spectra can be explained as the residual in symme”
Kimura 和 Ono - 2001 - Chelator-induced disappearance of carboxylate stre DOI: 10.1021/bi011216w -
Alkyl C-H confidence 1.0
“Likewise, the 1404 cm-1 peak confirms the presence of the C-H, C=C, C==N, and C-N stretching belonging to the alkane, alkene, primary and secondary amine, respectively;”
Green Energy Generated in Single-Chamber Microbial Fuel Cells Using Tomato Waste DOI: 10.3390/su151310461 -
Carboxyl (COOH) confidence 1.0
“A peak appears at 1546 for ν with a s(COO-) cm-1, corresponding high intensity ν peak at 1404 presumably associated with the distal-”
pH-Dependent Adsorption of α-Amino Acids, Lysine, Glutamic Acid, Serine and Glycine, on TiO2 Nanoparticle Surfaces DOI: 10.1016/j.jcis.2019.06.086 -
Nitrogen heterocycle confidence 1.0
“cm-1 Centeno and Shamir [48] attributed the 1404 band to pyrrole ring stretching and 1454 cm-1 cm-1 to C=C aromatic ring vibration, whereas Bridelli et al.”
Water-Activated Semiquinone Formation and Carboxylic Acid Dissociation in Melanin Revealed by Infrared Spectroscopy DOI: 10.3390/polym13244403 -
Amide confidence 1.0
“Peak at cm-1 1404and 1285 obtained was due to C-N stretching.”
Bhattacharyya 等 - 2017 - Metallization and APPJ treatment of bismaleimide DOI: 10.1155/2010/987357 -
Alkene (C=C) confidence 1.0
“The peaks at 1404 and 1541 cm-1 are assigned to the C=C H2O and NOx during the thermal decom-”
Bijanzad 等 - 2015 - Photocatalytic activity of mesoporous microbricks DOI: 10.1016/S1872-2067(14)60305-3 -
Carboxyl (COOH) confidence 1.0
“H asymmetric deformation of methyl agencies), at 1404 cm-1 (due to the COO-symmetric”
Fadlelmoula 等 - 2022 - Fourier Transform Infrared (FTIR) Spectroscopy to DOI: 10.3390/mi13020187 -
Acetate confidence 1.0
“The1416.1,1404.1cm-1 2 intoaccounttocalculate bandsobservedinthespectraofthecomplexinArmatrixareassignedtothe coupledδ(NOH)+δ(CH3)vibrations.”
Complexes of Formaldehyde and -Dicarbonyls with Hydroxylamine: FTIR Matrix Isolation and Theoretical Study DOI: 10.3390/molecules26041144
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