What absorbs at 1551 cm⁻¹ in an FTIR spectrum?
A band near 1551 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 1551 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 | 12 | 10 | 1.0 |
| N h | 4 | 4 | 1.0 |
| Carboxyl (COOH) | 3 | 3 | 1.0 |
| Secondary amine | 2 | 2 | 1.0 |
| Protein alpha helix | 2 | 2 | 1.0 |
| Alkyl C-H | 2 | 2 | 1.0 |
| Carbonyl (C=O) | 2 | 2 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Bromine | 1 | 1 | 1.0 |
| Alkene (C=C) | 1 | 1 | 1.0 |
| C=n | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| Protein beta sheet | 1 | 1 | 1.0 |
| Urethane | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Methacrylate | 1 | 1 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Acetate | 1 | 1 | 1.0 |
| Protein | 1 | 1 | 0.8 |
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 |
|---|---|---|---|
| gelatin | 1551, 1652, 3300 | Amide, N h | 1 |
| chitosan | 1551, 1650, 1655 | Amide, N h | 1 |
| polyurethane | 1551, 2270, 1700 | N h, Amide | 1 |
| ZnO | 1551, 1400, 3430 | Amide | 1 |
| graphene oxide | 1551, 1150, 3400 | Carboxyl (COOH) | 1 |
| Fe3O4 | 1551, 2358, 1673 | 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 1551 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
-
Acetate confidence 1.0
“O-H stretching 3494.77 3496.70 3494.77 3492.85 3434.98 3454.27 3436.91 vibration 2339.49 2360.71 2364.57 2360.71 2343.35 2341.42 2339.49 CO O-H stretching 3494.77 3496.70 3494.77 3492.85 3434.98 3454.27 3436.91 O-H stretching 3494.77 3496.7”
Harsono 等 - 2017 - Paramagnetic Zn(1-x)MnxO (0.00≤x≤0.06) Nanopar DOI: 10.4313/TEEM.2017.18.1.46 -
Ring structure confidence 1.0
“cm-1 bands at 1551 and 1519 are most likely primarily ring modes of ferrous heme a and the troughs at 1538 and 1501 documented34-36,48-51 also been well though are not yet well cm-1 loss of the corresponding ring modes of ferrous heme a 3.”
Iwaki 和 Rich - 2007 - An IR study of protonation changes associated with DOI: 10.1021/ja067779i -
Urethane confidence 1.0
“The aforementioned bond was detected and confirmed using cm-1 attenuated total reflectance-Fourier transform Infrared (ATR-FTIR) spectroscopy with two prominent peaks at 1551 3-), 2cm-1, 3+-R), (RNH-CO and 1709 corresponding to ionic organi”
Qaroush 等 - 2017 - Chemisorption of CO2 by chitosan oligosaccharideD DOI: 10.1039/C7GC01830D. -
Protein alpha helix confidence 1.0
“Nevertheless, Nevertheless, the the peaks peaks at at 1540, 1540, 1545, 1545, and and 1551 1551 cm-1 α-helical β-sheet usually assigned to structure, while the peaks at 1520 to 1525 are assigned to conformational sensitivity compared with a”
Sadat 和 Joye - 2020 - Peak Fitting Applied to Fourier Transform Infrared DOI: 10.3390/app10175918 -
Alkyl C-H confidence 1.0
“cm-1 C=C that is centered at 1620 The peak at 1551 (42.35 emu/g) indicates that the saturation magnetization may be belonged to =CH2 groups.”
Magnetic photocatalysts based on graphene oxide: synthesis, characterization, application in advanced oxidation processes and response surface analysis DOI: 10.1007/s13201-023-01931-4 -
Alkyl C-H confidence 1.0
“2 857cm-1, ging vibration at stretching vibrations at 3476 disappear with time as the condensation of the low-volatility 3380cm-1, 1551cm-1, and bending at and the CH wagdimer to the reactor surfaces takes place.”
Berasategui 等 - 2020 - Kinetic and mechanistic study of the reaction betw DOI: 10.5194/acp-20-2695-2020 -
Amide confidence 1.0
“LLM confirmed rule peak-group candidate”
Improved Protocols for Vibrational Spectroscopic Analysis of Body Fluids DOI: 10.1002/jbio.201300130 -
Aromatic ring confidence 1.0
“The absorption peaks mainly concentrated during 650 cm-1~1800 cm-1 and 2700 cm-1~3000 cm-1, cm-1~3000 cm-1, which were formed by the swinging vibration of H bond on benzene ring 2700 whichwereformed by theswinging vibrationof Hbond onbenzen”
Evaluation of Properties and Micro-Characteristics of Waste Polyurethane/Styrene-Butadiene-Styrene Composite Modified Asphalt DOI: 10.3390/polym13142249
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