What absorbs at 1556 cm⁻¹ in an FTIR spectrum?
A band near 1556 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 1556 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 | 11 | 9 | 1.0 |
| N h | 6 | 6 | 1.0 |
| C c single bond | 4 | 4 | 1.0 |
| Ring structure | 4 | 4 | 1.0 |
| Secondary amine | 3 | 3 | 1.0 |
| Alkyl C-H | 3 | 3 | 1.0 |
| Methacrylate | 3 | 3 | 1.0 |
| Acetate | 3 | 3 | 1.0 |
| Nitrogen heterocycle | 3 | 2 | 1.0 |
| Carboxyl (COOH) | 3 | 2 | 1.0 |
| Aromatic ring | 2 | 2 | 1.0 |
| Methoxy (OCH3) | 2 | 2 | 1.0 |
| C-O single bond | 2 | 2 | 1.0 |
| Alkene (C=C) | 2 | 1 | 0.9 |
| Borate | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| C=n | 1 | 1 | 1.0 |
| Protein | 1 | 1 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| Siloxane (Si-O-Si) | 1 | 1 | 1.0 |
| Silicon-oxygen (Si-O) | 1 | 1 | 1.0 |
| Metal oxygen | 1 | 1 | 0.9 |
| Carbonate | 1 | 0 | 1.0 |
| Thiol | 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 |
|---|---|---|---|
| ZnO | 1556, 1400, 3430 | Amide | 1 |
| polyaniline | 1556, 1565, 1570 | Amide, Ring structure | 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 1556 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
-
Alkyl C-H confidence 1.0
“The bands between 2850 and 2959 indicate alkyl C-H (asymmetric of cm-1 and symmetric) stretching, while signals at 1556 indicate CH scissoring.”
Structural analysis and antioxidative properties of mutan (water-insoluble glucan) and carboxymethyl mutan from Streptococcus mutans DOI: 10.1016/j.procbio.2020.07.006 -
confidence 1.0
“Results and Discussion Si-O asymmetric stretching in -Si-O-Si-, and a peak around 1556 cm-1, which”
Surface Heparinization of a Magnesium-Based Alloy: A Comparison Study of Aminopropyltriethoxysilane (APTES) and Polyamidoamine (PAMAM) Dendrimers DOI: 10.3390/jfb13040296 -
Ring structure confidence 1.0
“The cm-1 cm-1 17 absorptions at 1556 and 1479 are assignable to the ring stretching vibration of quinoid (Q)”
Multimorphologies of Hydrochloride Polyaniline Synthesized by Conventional and Interfacial Polymerization DOI: 10.1016/j.molstruc.2017.04.104 -
Alkyl C-H confidence 1.0
“The peaks at 2,925 and 2,850 Both POXC and SOC were mainly showing positive cm-1 showed weakly positive coefficients for both POXC and regression coefficients with the band at 1556 C-H SOC and are attributed to aliphatic stretching”
Identifying the fingerprint of permanganate oxidizable carbon as a measure of labile soil organic carbon using Fourier transform mid‐infrared photoacoustic spectroscopy DOI: 10.1111/ejss.13085 -
confidence 1.0
“In the FT-IR spectra of pure and Mn-doped (1%, structure of ZnO NPs and Mn-doped ZnO nanoparticles (Pathak 2.5%,5%,and7%)ZnOnanoparticles,typicalpeakswereobservedat 3442cm-1, 1556cm-1, 1338cm-1, 1080cm-1, 825-665cm-1.”
Khan 等 - 2022 - Microwave-Assisted Green Synthesis of Pure and Mn- DOI: 10.3389/fmats.2021.710155 -
Acetate confidence 1.0
“The 0:100 cm-1 cm-1 AMD:AMN (100% AMN) salt showed the new peaks at 1556 and 1385 which were assigned as asymmetric and symmetric C=O stretching of carboxylate, respectively, while the cm-1 relative absorbance of the peak at 1716 declined.”
Meenabun 等 - 2010 - Effect of 2-Amino 2-methyl 1,3 propanediol on Ente DOI: 10.4028/www.scientific.net/AMR.93-94.467 -
C c single bond confidence 1.0
“The peaks at 3433 is corresponds to N H 738, 584, 509 & 422 cm-1 is for stretching vibration of C C bonds of quiniod rings, stretching vibration 1556 04 14:53 at Laval] [Universite by Downloaded Figure 1.”
Patil 等 - 2011 - Electrical Conductivity of PolyanilineNiZnO3 Comp DOI: 10.1080/00150193.2011.620836 -
Carboxyl (COOH) confidence 1.0
“downward-pointingpeakat1704cm-1(attributabletocarboxylic at 2715 the more prominent shoulder at 2810 and cm-1, the intense carbonyl at 1729 aciddeprotonation)isaccompaniedbythegrowthinanupwardalong with their narrowcm-1 pointing peak of car”
Razgon 等 - 2008 - Ozonolysis-based route to the in situ formation of DOI: 10.1021/la703120c
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