What absorbs at 744 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 744 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.

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 744 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

• Phosphate (PO4) confidence 1.0

  “LLM confirmed rule peak-group candidate”

  Structural and morphological characterization of Pr3+ and Er3+-containing SiO2–P2O5 sol–gel thin films DOI: 10.1016/j.matchemphys.2011.10.031
• Silicon silicon confidence 1.0

  “The peaks at 1139.24 cm-1 and 1095.99 cm-1 are assigned to stretching vibration of Si-O, the peaks at 1031.25 cm-1 and 1008.16 cm-1 are assigned to stretching vibration of Si(Al)-O, the peaks at 787.56 cm-1 and 761.71 cm-1 are assigned to s”

  Effects and Mechanism of Fe3+ on Flotation Separation of Feldspar and Epidote with Sodium Oleate at Natural pH DOI: 10.3390/separations9050110
• Amide confidence 1.0

  “Similarly, the stretching vibration at 714.54 cm-1 (AM-5), 773.99 cm-1 (AM-7), and 744.0 cm-1 (AM-8) represented the C-N-C out-of-plane bending of the imine formed.”

  Novel Hemocompatible Imine Compounds as Alternatives for Antimicrobial Therapy in Pharmaceutical Application DOI: 10.3390/pr8111476
• Silicon (Si) confidence 1.0

  “cm-1 The bands at 744 and 687 are attributed to the perpendicular Si-O stretching vibration.”

  Morphology and Selected Properties of Modified Potato Thermoplastic Starch DOI: 10.3390/polym15071762
• Alkene (C=C) confidence 1.0

  “3 cm-1 cm-1 1124, 1073, 1040, 952 (generally, C-O stretch), and 744 (C=C-H bend) [25-27].”

  Identification of Colourants and Varnishes in a 14th Century Decorated Wood-Carved Door of the Dionysiou Monastery in Mount Athos DOI: 10.3390/coatings11091087
• Carbonate confidence 1.0

  “The ν4 in-plane bending mode at 713 cm-1 and 744 cm-1 are assigned to calcite and vaterite, respectively,”

  Investigating the Potential of the Er:YAG Laser for the Removal of Cemented Dust from Limestone and Painted Plaster DOI: 10.3390/coatings10111099
• confidence 1.0

  “Peaks at 744 and 460 are due to external tetrahedral cm-1 Zn-O22,23.”

  Mesoporous ZnAl2Si10O24 nanofertilizers enable high yield of Oryza sativa L. DOI: 10.1038/s41598-020-67611-4
• Alkyl C-H confidence 1.0

  “FTIR spectra shown in Figure 9 reveal peaks of C=C bending at 684 cm-1, C-H bending at 744 cm-1, C-H bending at 818 cm-1, C-H bending at 872 cm-1, C-N stretching aromatic amine at 1261 cm-1, C-C stretching aromatic ring at 1493 cm-1, C=C st”

  Synthesis of a Polyaniline Nanoparticle Using a Solution Plasma Process with an Ar Gas Bubble Channel DOI: 10.3390/polym11010105