What absorbs at 1398 cm⁻¹ in an FTIR spectrum?
A band near 1398 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 1398 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 | 8 | 8 | 1.0 |
| Amide | 6 | 6 | 1.0 |
| Methacrylate | 5 | 5 | 1.0 |
| Acetate | 5 | 5 | 1.0 |
| Carboxyl (COOH) | 4 | 4 | 1.0 |
| Carbonyl (C=O) | 3 | 3 | 1.0 |
| Methoxy (OCH3) | 3 | 3 | 1.0 |
| Secondary amine | 3 | 3 | 1.0 |
| C n single bond | 3 | 3 | 1.0 |
| Protein | 2 | 2 | 1.0 |
| Ketone | 2 | 2 | 1.0 |
| Ester | 2 | 2 | 1.0 |
| Methyl | 2 | 2 | 1.0 |
| N h | 2 | 2 | 1.0 |
| Fatty acid | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Protein beta sheet | 1 | 1 | 1.0 |
| Lipid | 1 | 1 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Sulfur heterocycle | 1 | 1 | 1.0 |
| C-S single bond | 1 | 1 | 1.0 |
| Carbonate | 1 | 1 | 0.9 |
| C=n | 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 |
|---|---|---|---|
| polypropylene | 1398, 1030, 1600 | Alkyl C-H, Methacrylate, Acetate | 1 |
| polyaniline | 1398, 1565, 1570 | Amide, Alkyl C-H, Methacrylate | 1 |
| nanocomposites | 1398, 1717, 1630 | 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 1398 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
-
C-S single bond confidence 1.0
“After polymerization of the aniline moiety, sharp of cm-1 peaks representing C N and C S appeared at 1398 and 617 stretching vibrations, respectively.”
Stopband attenuation of silica spheres by attaching aniline and polyaniline DOI: 10.1016/j.synthmet.2013.03.007 -
Amide confidence 1.0
“The band III represents the vibrations in 1000 to 2000 cm-1 cm-1 is attributed to C N [16, 17] and the peak at 1398 absorption peak at 1591 cm-1 C-C of sp3 corresponds to amorphous bonds [18].”
Ramesh 等 - 2010 - Synthesis of Nano Structured Carbon Nitride by Pyr DOI: 10.1080/10584587.2010.489421 -
Sulfur heterocycle confidence 1.0
“Synthesis of PMOT/NiO nanocomposite The band thiophene ring were found at 1576 and 1398 cm-1 at 1092 has been identified as the stretching vibration of”
Sehgal 和 Narula - 2015 - Structural, morphological, optical, and electrical DOI: 10.1007/s00396-015-3663-z -
Alkyl C-H confidence 1.0
“cm-1 1157 were assigned to the C-H bending vibration of collagen peptide and asymmetric stretching The peaks around 1398 cm-1 and 1157 cm-1 were assigned to the C-H bending vibration of collagen”
Sponges of Carboxymethyl Chitosan Grafted with Collagen Peptides for Wound Healing DOI: 10.3390/ijms20163890 -
Alkyl C-H confidence 1.0
“95 92 C-H stretching Alkyne ** 1398 99 95 90 O-Hbending Carboxylicacid 1543 99 94”
A Comparison of Water Imbibition and Controlled Deterioration in Five Orthodox Species DOI: 10.3390/agronomy12071486 -
Lipid confidence 1.0
“This was based on PC-2, which was driven by differences in the 1740 1 lipid peak, the relative enrichment of β-sheets in the DJX species, and differences in the width cm-1 of the 1398 peak.”
Synchrotron FTIR as a tool for studying populations and individual living cells of green algae DOI: 10.1101/808220 -
Alkyl C-H confidence 1.0
“cm-1, the aromatic C=C bond is tenuously situated at 1602 and 1491 At 1398 cm-1, there is a corresponding deformed CH and CH absorption band.”
Valoration of the Synthetic Antioxidant Tris-(Diterbutyl-Phenol)-Phosphite (Irgafos P-168) from Industrial Wastewater and Application in Polypropylene Matrices to Minimize Its Thermal Degradation DOI: 10.3390/molecules28073163 -
Amide confidence 1.0
“The cm-1, cm-1 cm-1 peaks entered at 1398 1025 and 661 can be associated with C-N stretching of amine, alcohol/phenolic stretching, and aromatic C-H bending (Manikandan et al.”
Application of mycogenic silver/silver oxide nanoparticles in electrochemical glucose sensing; alongside their catalytic and antimicrobial activity DOI: 10.1007/s13205-021-02888-4
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.