What absorbs at 3670 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 3670 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 3670 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

  “Nominal end-member rubidium richterite is assigned to the arrangement MgMgMg-OH-Rb and the cm-1 minor band at 3670 is assigned to the arrangement MgMgMg-OH-□ X A-site For the nominal "Rb-richterite" = 0.0 end-member comwith vacancy at the (”

  Synthesis and solid solution in “rubidium richterite”, Rb(NaCa)Mg5Si8O22(OH,F)2 DOI: 10.1007/s00269-019-01037-x
• Hydroxyl (O-H) confidence 1.0

  “The narrow O-H cm-1 stretching modes at ~3670 (Figure 4) are very specific and fit well with asbestos.”

  Asbestos-Based Pottery from Corsica: The First Fiber-Reinforced Ceramic Matrix Composite DOI: 10.3390/ma13163597
• Silanol (Si-OH) confidence 1.0

  “Its overtone (ν 2) is visible at 2260 along 243 cm-1, with the Si-OH symmetric and antisymmetric stretching mode at 3670 useful to monitor the OH content [1].”

  Cova 等 - 2021 - Influence of the fiber drawing process on mechanic DOI: 10.1016/j.jnoncrysol.2020.120534
• Hydroxyl (O-H) confidence 1.0

  “The signal for end-OH stretching of PCHC appeared near 3670 cm-1;”

  Du 等 - 2022 - Intraand Intermolecular Hydrogen Bonding in Misc DOI: 10.3390/ijms23137018
• Hydroxyl (O-H) confidence 1.0

  “stretching mode of water (~3100 and the surface Ge-OH band (~3670 A much weaker”

  Effects of Temperature on the Morphology and Optical Properties of Spark Discharge Germanium Nanoparticles DOI: 10.3390/ma13194431
• Water (H2O) confidence 1.0

  “vibrations at 3670 and 3657 These bands are due to water molecules present in the region surrounded by Thr46, Asp96 and Phe219.”

  Morgan 等 - 2007 - Water structural changes in the L and M photocycle DOI: 10.1021/bi0616596.
• Hydroxyl (O-H) confidence 1.0

  “The additional bands around 3670 and 3544 assigned to OH modes of slightly perturbed H 2O molecules (labelled as (b) and (c) in Scheme 1).”

  Negri 等 - 2018 - Investigating the Low Temperature Formation of Cu- DOI: 10.1002/chem.201802769
• Metal oxygen confidence 1.0

  “3691 - 89 3688 3688 3688 3688 3686 3688 3688 3688 3686 hydroxyl groups Al-O-H stretching of inner surface 3669 3669 3670 3670 3670 3670 3670 3670 3670 3670 hydroxyl groups Al-O-H stretching of inner surface”

  Oyebanjo 等 - 2018 - Mineral Constituents and Kaolinite Crystallinity o DOI: 10.1515/geo-2018-0012