What absorbs at 1305 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 1305 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 1305 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

• Alkene (C=C) confidence 1.0

  “1305, and These peaks correspond to a C=C stretching viphosphate adsorption decreased, compared with the initial pH, because bration of the quinoid ring, a C=C stretching vibration of the benze-”

  A facile polymerisation of magnetic coal to enhanced phosphate removal from solution DOI: 10.1016/j.jenvman.2019.06.088
• Carbonyl (C=O) confidence 1.0

  “The band at 1305 is associated with the carbonyl group of the ketone linkage in the cm-1 PEEK repeat unit, while the band at 1280 is observed due to the resonance of the”

  Vibrational spectroscopic study of pure and silica-doped sulfonated poly(ether ether ketone) membranes DOI: 10.1016/j.saa.2014.12.004
• Alkyl C-H confidence 1.0

  “As the tem- ◦C, cm-1 reaction starts to occur at 225 as highlighted by the appearance of the band at 1305 perature increases, the methanation reaction starts to occur at 225 °C, as highlighted by (C-H degenerate bending, gas-phase methane [”

  Thermal and Plasma-Assisted CO2 Methanation over Ru/Zeolite: A Mechanistic Study Using In-Situ Operando FTIR DOI: 10.3390/catal13030481
• Alkyl C-H confidence 1.0

  “The bending oscillation of the C-H group in the aldehydes was disclosed by the band at 1305 whereas the C-O pulling oscillations of the cm-1, hydes was disclosed by the band at 1305 cm-1, whereas the C-O pulling oscillations of the ether an”

  Green Synthesis of TiO2 Nanoparticles Using Acorus calamus Leaf Extract and Evaluating Its Photocatalytic and In Vitro Antimicrobial Activity DOI: 10.3390/catal12020181
• Acetate confidence 1.0

  “C-H stretching in -CH3 and -CH2 at 2933, 2895, and 2855 cm-1), C=O stretching in esters (1750 cm-1), C=C stretching (1660 cm-1), CH2, and CH3 deformations (1460-1440 and 1305 cm-1), and C-C and C-O stretching (1080-1060 cm-1).”

  Assessment of Biotechnologically Important Filamentous Fungal Biomass by Fourier Transform Raman Spectroscopy DOI: 10.3390/ijms
• Ester confidence 1.0

  “The observed spectra (Figure 14) cm-1 display two bands between 1305 and 1055 that correspond to the symmetric and cm-1 asymmetric stretches of the ester group of Irgafos P-168 and a peak at roughly 1737 that is suggestive of the ester grou”

  Valoration of the Synthetic Antioxidant Tris-(Diterbutyl-Phenol)-Phosphite (Irgafos P-168) from Industrial Wastewater and Application in Polypropylene Matrices to Minimize Its Thermal Degradation DOI: 10.3390/molecules28073163
• Alkyl C-H confidence 1.0

  “carbohydratemoietyofmucus.20 (symmetric and antisymmetric Theabsenceofdifferencesnear of 2850 and 2922 2) are assigned to lipids, in particular stretch vibrations of CH lipidandhemoglobinbandsindicatesthattheseconstituentsdid phospholipids.”

  Krafft 等 - 2008 - Raman mapping and FTIR imaging of lung tissue con DOI: 10.1039/b712958k
• Acetate confidence 1.0

  “[32] C-O stretching 1038 and 1079 S-C-H bending 1209 and 1249 R-C=O stretching 1305, 1500-1750 R=C=O stretching”

  Kravanja 和 Finsgar - 2021 - Analytical Techniques for the Characterization of DOI: 10.3390/biomedicines9121936