What absorbs at 1218 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 1218 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 1218 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

  “Weak bands at 1218 and 1088 indicate the presence of C-H and C-O stretching of alcohols, carboxylic acids, ester and, ether groups respectively.By comparing the spectrum of the as iron oxide nanoparticles each other, Fig.”

  Green Synthesis of Iron Oxide Nanoparticles by Aqueous Leaves Extract of Mentha Pulegium .L: Effect of Ferric Chloride Concentration on The Type of Product DOI: 10.1016/j.matlet.2020.127364
• Alkyl C-H confidence 1.0

  “(2020), the to O-H stretch, while the peaks at 2972, 1375, and 1218 cm-1 heating process to diatomite waste at 400 °C increases could be attributed to C-H stretching vibration.”

  Hamdiani 和 Shih - 2021 - A Green Method for Synthesis of Silver-Nanoparticl DOI: 10.22146/ijc.63573
• Amide confidence 1.0

  “Summary of molecular vibration of PBS chromophore (cm-1) Group Wavenumber, 𝝂 700 C-H bending 754 C-H bending of 776 C-H bending 1079 S=O stretching Pre-pro 1218 C-N stretching 1289 C-N stretching 1330 S=O stretching 1402 S=O stretching 1427”

  Power-Dependent Nonlinear Optical Behaviours of Ponceau BS Chromophore at 532 nm via Z-Scan Technique DOI: 10.1016/j.jphotochem.2020.112574
• Alkyl C-H confidence 1.0

  “C-H stretching vibration of 1218cm(cid:1)1 As3þ in treated samples indicated the alkyl chains that attributed to the presence of As3þ presence of polysaccharides in the EPS samples.”

  Saba 等 - 2019 - Potential role of bacterial extracellular polymeri DOI: 10.1080/10889868.2019.1602107
• Acetate confidence 1.0

  “In addition, a C=O peak observed at 1699 The peaks appearing at 1218 cm-1 belonged to the C-O stretching of the ester group in all cm-1, in addition to a peak at 1413 corresponded to the CH detected in all samples.”

  Structural Conformation Comparison of Different Clear Aligner Systems: An In Vitro Study DOI: 10.3390/dj10050073
• Alkyl C-H confidence 1.0

  “The intensity of the C-O-C band at 960-900 cm-1, corresponding to the C-H out-of-plane bending of the benzene and the O-C cm-1 band at 1218 is reduced after 30 min and the reduction becomes more pronounced after 60 min.”

  Arslan 等 - 2018 - Ring-Opening Polymerization of 1,3-Benzoxazines vi DOI: 10.3390/polym10030239
• Amide confidence 1.0

  “The stretching vibration at 1225-1218 corresponds to the cm-1 C-N linkage [33,36] in the urethane group, while the band at 1218 is assigned to S and G ring breathing in lignin [37], with both bands visible in all three formulations”

  Synthesis and Characterizations of Eco-Friendly Organosolv Lignin-Based Polyurethane Coating Films for the Coating Industry DOI: 10.3390/polym14030416
• Carboxyl (COOH) confidence 1.0

  “Indeed the bands at 1218 and 1280 can be [43,44]underambientlightduringthe24hdryingofthepaint(see n(C-O) attributed to of carboxylic acids radiooxidative products.”

  A FTIR/chemometrics approach to characterize the gamma radiation effects on iodine/epoxy-paint interactions in Nuclear Power Plants DOI: 10.1016/j.aca.2017.01.005