What absorbs at 1557 cm⁻¹ in an FTIR spectrum?
A band near 1557 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 1557 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 | 6 | 5 | 1.0 |
| N h | 3 | 3 | 1.0 |
| Ring structure | 3 | 3 | 1.0 |
| Alkyl C-H | 3 | 3 | 1.0 |
| Ester | 3 | 3 | 1.0 |
| Carboxyl (COOH) | 3 | 3 | 1.0 |
| Carbonyl (C=O) | 3 | 3 | 1.0 |
| Aromatic ring | 2 | 2 | 1.0 |
| Methacrylate | 2 | 2 | 1.0 |
| Ketone | 2 | 2 | 1.0 |
| Acetate | 2 | 2 | 1.0 |
| Protein | 2 | 1 | 1.0 |
| Bromine | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Alkene (C=C) | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Metal oxygen | 1 | 1 | 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 |
|---|---|---|---|
| lignin | 1557, 1035, 1510 | Alkyl C-H | 1 |
| GO | 1557, 1720, 1182 | Alkyl C-H, Amide | 1 |
| RGO | 1557, 2358, 2930 | Alkyl C-H, Amide, N h | 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 1557 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
-
confidence 1.0
“cm(cid:3)1 The bands at 1121-1328 are due to the stretching vibration and deformation cm(cid:3)1 vibration characteristics of SO and band at 1556.73 is the characteristic of 2 SDBS.7 absorption peak of There are wide and high peaks of Al-O”
Mirjalili 等 - 2013 - The effect of dispersant on toughening mechanism a DOI: 10.1177/0892705712454288 -
Acetate confidence 1.0
“1735 0.087 C=O stretching - 1557 0.089”
Removal of Uranium and Associated Contaminants from Aqueous Solutions Using Functional Carbon Nanotubes-Sodium Alginate Conjugates DOI: 10.3390/min6010009 -
Hydroxyl (O-H) confidence 1.0
“1113 For RGO, the -OH vibrations peak is almost cm-1 disappeared and an intense peak at 1557 appeared, corresponding to the C=C stretching in the graphitic ring”
Reduced graphene oxide-intercalated graphene oxide nano-hybrid for enhanced photoelectrochemical water reduction DOI: 10.1007/s40097-019-00324-x -
confidence 1.0
“-CN C-C band's absence at around 2250 due to the stretch with C=O stretching vibrations, and aromatic ring chain cm-1.46 vibrations were observed at 1590 The modification by that no unreacted cyano groups remained on the sample surface.19,2”
Bouchmella 等 - 2023 - Impact of Mesoporous Silica Functionalization Fine DOI: 10.1021/acsomega.2c08065 -
confidence 1.0
“The XRD spectrum of Agr shows a peak 19.1◦ ∼ 2θ 1556.6 cm-1 and 1404.6 cm-1, N-H out of plane wagging at 608.8 cm-1, and C-H stretching at 928.2 at with the intensity of 1624 (a.u), which demonstrates the semi-crystalline nature of ∼ at 2θ”
Development of Biodegradable Agar-Agar/Gelatin-Based Superabsorbent Hydrogel as an Efficient Moisture-Retaining Agent DOI: 10.3390/biom10060939 -
Carboxyl (COOH) confidence 1.0
“LLM confirmed rule peak-group candidate”
Synthesis and Application of Tackifying Dispersant Poly (Vinyl Alcohol-Acrylic Acid-Triallyl Cyanate) DOI: 10.3390/polym14030557 -
Ester confidence 1.0
“cm-1, presence of the carbonyl group, found at 1557 corresponding to the ester formation of the C-H bonds in the methyls and methylenes of the hydrocarbon chains, as well as the of the C-H bonds in the methyls and methylenes of the hydrocar”
Lauroylated, Acetylated, and Succinylated Agave tequilana Fructans Fractions: Structural Characterization, Prebiotic, Antibacterial Activity and Their Effect on Lactobacillus paracasei under Gastrointestinal Conditions DOI: 10.3390/polym15143115 -
Protein confidence 1.0
“The relative intensities of as well as in the protein bands (1645 cm-1 and 1557 cm-1), although no correspondence with the total C.”
Fornito 等 - 2020 - Degradative Ability of Mushrooms Cultivated on Cor DOI: 10.3390/molecules25133020
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