What absorbs at 1581 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 1581 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

Ranking reflects accumulated literature evidence, not a single fixed rule. Always confirm against your sample context.

Possible materials

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 1581 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

  “LLM confirmed rule peak-group candidate”

  Ionic liquid assisted hydrothermal synthesis of TiO2 nanoparticles: photocatalytic and antibacterial activity DOI: 10.1016/j.jmrt.2017.02.001
• Aromatic ring confidence 1.0

  “These Raman lines are atFigure 5a-c have maxima at ~415-498 cm-1, 621-825 cm-1, 906-1003 cm-1, 1184 cm-1, 1331 C=N stretching, C=C stretching in the quinoid ring and C-C stretching in the benzene ring, tributed to the vibrational modes caus”

  The Photoluminescence and Vibrational Properties of Black Phosphorous Sheets Chemically/Electrochemically Functionalized in the Presence of Diphenylamine DOI: 10.3390/polym14214479
• confidence 1.0

  “deformations of the amine bound to the metal-0.933 for 1589/1581cm-1 1586cm-1 A red shift of the amine scissoring modes, occurring at (Raman), 1588/1573cm-1 (FTIR) and (INS), was detected relative to the free diaminopropane ligand and simil”

  Batista de Carvalho 等 - 2012 - Pt(II) Complexes with Linear Diamines-Part I Vibr DOI: 10.1155/2012/206297
• N h confidence 1.0

  “After the peaks, the spectrum of PANI exhibits peaks at 684 and 1581 cm-1, desorption, NZC-g-PANI was washed with a 0.1 N HCl which may be related to NH wagging and the presence 2 group.39 solution followed by drying for reuse in the adsorp”

  Bir 等 - 2022 - Multifunctional Ternary NLPZnO@L-cysteine-grafted DOI: 10.1021/acsomega.2c04936
• Carboxyl (COOH) confidence 1.0

  “cm(cid:2)1 features near 3300 and 1650 due to 'MOH affected' at2340cm(cid:2)1 and 7.(c)Plotsof CO absorbance fromtheexperiments 2 water,20,49 bulk and the solution formate bands near 1581, 1382 depicted in Fig.”

  Christensen 等 - 2011 - The electro-oxidation of formate ions at a polycry DOI: 10.1039/c1cp20166b
• Acetate confidence 1.0

  “The procedure was regularly trumalso displays barely detectablefeaturesat1669and 1581 cm-1 carried out in presence of inert and porous materials and, respectively assigned to C=O (amide I) and a combinaamong those, bones ash was commonly us”

  The combined use of SEM-EDX, Raman, ATR-FTIR and visible reflectance techniques for the characterisation of Roman wall painting pigments from Monte d’Oro area (Rome): an insight into red, yellow and pink shades DOI: 10.1007/s11356-021-15085-w
• Carbonyl (C=O) confidence 1.0

  “New small peaks at 1581 0 25 50 75 100 125 150 2-Mn+ cm-1 and 1556 are due to the ν(C=O) from -CO (M = Z (Ω) nature,17 Re Li/Ti) with different chemical bonding which may be the decomposition product of BMP cation combined with oxy-”

  Kim 等 - 2011 - Study on the Cycling Performance of Li4Ti5O12 Elec DOI: 10.5012/bkcs.2011.32.1.105
• Acetate confidence 1.0

  “CHF spectrum also exhibited 1653cm-1 the distinctive absorption bands at (C O stretching 1581cm-1 (-NH bendin amide group, amide I vibration) and 2 inginnon-acetylated2-aminoglucoseprimaryamine).Absorption bandsat1158cm-1(antisymmetricstret”

  Rivero 等 - 2010 - Crosslinking capacity of tannic acid in plasticize DOI: 10.1016/j.carbpol.2010.04.048