What absorbs at 1538 cm⁻¹ in an FTIR spectrum?
A band near 1538 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 1538 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 |
|---|---|---|---|
| Amide | 25 | 22 | 1.0 |
| N h | 11 | 10 | 1.0 |
| Secondary amine | 8 | 7 | 1.0 |
| Carboxyl (COOH) | 7 | 7 | 1.0 |
| Carbonyl (C=O) | 6 | 6 | 1.0 |
| Methacrylate | 5 | 4 | 1.0 |
| Acetate | 5 | 4 | 1.0 |
| C n single bond | 4 | 4 | 1.0 |
| Ketone | 4 | 4 | 1.0 |
| Ester | 4 | 4 | 1.0 |
| N-O bond | 2 | 2 | 1.0 |
| C c single bond | 2 | 2 | 1.0 |
| N n bond | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| Nitro (NO2) | 1 | 1 | 1.0 |
| Alkyl C-H | 1 | 1 | 1.0 |
| Nitrogen heterocycle | 1 | 1 | 1.0 |
| Phosphorus | 1 | 1 | 1.0 |
| Phosphate (PO4) | 1 | 1 | 1.0 |
| Protein | 1 | 1 | 0.9 |
| Methoxy (OCH3) | 1 | 0 | 1.0 |
| C-O single bond | 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 |
|---|---|---|---|
| polypyrrole | 1538, 1700, 400 | Amide, Secondary amine, N h | 1 |
| bio-based | 1538, 1720, 1740 | Amide, Carboxyl (COOH), N h | 1 |
| polyaniline | 1538, 1565, 1570 | Amide, Secondary amine | 1 |
| copolymer | 1538, 2921, 1540 | Amide, Carboxyl (COOH) | 1 |
| dentin | 1538, 575, 1740 | Amide, Carboxyl (COOH) | 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 1538 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 c single bond confidence 1.0
“1543 C C stretching in quinoid rings C stretching in quinoid rings 1290 C N stretching 1538 C 1447 C C stretching in benzoid rings 2996”
Dey Sadhu 等 - 2020 - Preparation and characterization of polyanilinea DOI: 10.1002/pc.25738 -
Phosphate (PO4) confidence 1.0
“amide II (1538 and phosphate bands (1025 < group means, with statistical significance set at p 0.05.”
Root canal hydrophobization by dentinal silanization: Improvement of siliconbased endodontic treatment tightness DOI: 10.1002/jbm.b.32874 -
Amide confidence 1.0
“Amide I C=O Stretching Protein N-H, C-N 1538 Amide II In plane banding and stretching Protein O-C-H;”
Qualitative and Quantitative Analysis of Sorghum Grain Composition Including Protein and Tannins Using ATR-FTIR Spectroscopy DOI: 10.1007/s12161-020-01874-5 -
Amide confidence 1.0
“cm-1 (GP-SPF and Absorption bands for amide II at 1538 cm-1”
Manesa 等 - 2022 - Fabrication and Characterization of Sericin-PVA Co DOI: 10.1021/acsomega.2c00897 -
Nitrogen heterocycle confidence 1.0
“LLM confirmed rule peak-group candidate”
Munot 等 - 2019 - Electrochemical Investigations on Semi-conducting DOI: 10.4152/pea.201901043 -
confidence 1.0
“Polymers2023,15,1154 5of14 cm-1 cm-1 stretching), 1538 (N-H bending) and 1230 (C-N stretching) [12,22,23].”
Effects of NCO/OH Ratios on Bio-Based Polyurethane Film Properties Made from Acacia mangium Liquefied Wood DOI: 10.3390/polym15051154 -
Carbonyl (C=O) confidence 1.0
“1548 (cid:238)(C 1) 1538 cm-1, the only carbonyl stretch band The band at 1714 reduced 2dO)”
Wille 等 - 2003 - Redox-triggered FTIR difference spectra of FAD in DOI: 10.1021/bi035219f -
Alkyl C-H confidence 1.0
“In addition, a week and wide peak at 3200-3400 (N-H, ν, free 1 1 cmcm- (= imine groups), a week peak at 3080 C-H, ν), and two peaks at 1538 (N-H, 1 cmδ) and 1256 (C-N, ν) were detected attributing to PANi [9, 36].”
Arbab Solimani 等 - 2023 - Carboxymethyl Chitosan-Functionalized Polyaniline DOI: 10.1007/s12010-023-04526-6
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