What absorbs at 700 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 700 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 700 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

• Hydroxyl (O-H) confidence 1.0

  “For modified acetone, toluene, DMF and THF samples, the chemical decomposition peak is extended to ~700°C, which can be due to either higheramountofchemicalgraftingordehydroxylationoftheunreacted confirmed modified hydroxyl groups.”

  Silane functionalization of sodium montmorillonite nanoclay_ The effect of dispersing media on intercalation and chemical grafting DOI: 10.1016/j.clay.2017.12.020
• Acetate confidence 1.0

  “Additionally, peaks at 700.25, 666.92 and cm1 1075.51, 1039.62 indicate C-O stretch of the alcohol and ether group, respectively, while the vibration at cm-1 C≡C 2076.29 and 2069.54 demonstrates stretch of alkynes.”

  Antibacterial efficacy of synthesized silver nanoparticles of Microbacterium proteolyticum LA2(R) and Streptomyces rochei LA2(O) against biofilm forming meningitis causing microbes DOI: 10.1038/s41598-023-30215-9
• Hydroxyl (O-H) confidence 1.0

  “cm-1 Deconvolution of the Peak between 1750-1550 According to literature [35], moisture causes the occurrence of multiple peaks at following cm-1 wavenumbers: 700 (out-of-plane vibrations of O-H groups or rotational vibrations of the whole”

  IR Study on Cellulose with the Varied Moisture Contents: Insight into the Supramolecular Structure DOI: 10.3390/ma13204573
• Alkyl C-H confidence 1.0

  “1″-H 2′, 2″-H) confirming C-H and 2, are giving cross peaks that there is The peaks at 1002, 966, 909 and are due to wagging of 1′, 1″-H 2′, 2″-H C-H C-H magnetization transfer between 1, and 2, through the vinyl, wagging of trans, CH waggi”

  Reactive grafting of 3-octanoylthio-1-propyltriethoxysilane in styrene butadiene rubber_ Characterization and its effect on silica reinforced tire composites DOI: 10.1016/j.polymer.2019.121693
• confidence 1.0

  “In addition, the presence of a small peak around 700 can be Polymers2023,15,971 11of21 α-ferric attributed to the decomposition of Fe 3O to other compounds such as oxide [54].”

  Formulation and Characterization of Fe3O4@PEG Nanoparticles Loaded Sorafenib; Molecular Studies and Evaluation of Cytotoxicity in Liver Cancer Cell Lines DOI: 10.3390/polym15040971
• Ring structure confidence 1.0

  “IntheIberiansamplethecharacteristicsignalsofthearomatic 1606cm-1, rings, especially those of symmetric ring stretch 700cm-1) although out-of-plane ring bend loop (822, 755 and are even stronger probably due to the higher level of dehydroFig”

  Font 等 - 2007 - Fourier transform infrared spectroscopy as a suita DOI: 10.1016/j.aca.2007.07.021
• Silicon nitrogen confidence 1.0

  “absorption band between 700 SiON films with low oxygen incorporation have a peak wavenumber of the Si-N/Si-O absorption band similar to that of SiN, and this region of the absorption spectrum is heavily dominated”

  Effect of PECVD silicon oxynitride film composition on the surface passivation of silicon wafers DOI: 10.1016/j.solmat.2011.09.052
• Borate confidence 1.0

  “The sharp band at 700 was assigned to 6 the bending vibrations of B-O-B units in BO triangles [26].”

  Red light Emission from Europium doped Zinc Sodium Bismuth Borate Glasses DOI: 10.1016/j.physb.2017.09.113