What absorbs at 2905 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 2905 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 2905 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

  “At 2905 cm-1, the band analogous to C-H asymmetric stretching occurs [36].”

  Innovative Green Chemistry Approach to Synthesis of Sn2+-Metal Complex and Design of Polymer Composites with Small Optical Band Gaps DOI: 10.3390/molecules27061965
• Carbonyl (C=O) confidence 1.0

  “broadband at 3860 cm-1, characteristic intense bands corresponding to the asymmetrical and cm-1 Another group of signals associated with the cutin matrix is that from 1600 to 1750 attributed C=O symmetrical stretching vibrations of the meth”

  Cutin from Solanum Myriacanthum Dunal and Solanum Aculeatissimum Jacq. as a Potential Raw Material for Biopolymers DOI: 10.3390/polym12091945
• Alkyl C-H confidence 1.0

  “Bands corresponding to asymmetric and symmetric C-H stretching vibrations of aliphatic -CH2 groups were observed at 2905 and 2860 cm-1 respectively (Figure 3).”

  Branched Polyurethanes Based on Synthetic Polyhydroxybutyrate with Tunable Structure and Properties DOI: 10.3390/polym10080826
• Alkyl C-H confidence 1.0

  “to 2970 and the CH band between 2905 and 2945 To further observe the relative lipid/protein content in”

  Biophysical Stress Responses of the Yeast Lachancea thermotolerans During Dehydration Using Synchrotron-FTIR Microspectroscopy DOI: 10.3389/fmicb.2020.00899
• Hydroxyl (O-H) confidence 1.0

  “in the OH-stretching region, two broad bands are observed, centered at 2905 cm-1, and 2415 respectively (Figure 8).”

  Neutron and XRD Single-Crystal Diffraction Study and Vibrational Properties of Whitlockite, the Natural Counterpart of Synthetic Tricalcium Phosphate DOI: 10.3390/cryst11030225
• Alkyl C-H confidence 1.0

  “LLM confirmed rule peak-group candidate”

  Cheng 等 - 2018 - A new approach to improve mechanical properties an DOI: 10.1016/j.conbuildmat.2018.05.134
• Alkyl C-H confidence 1.0

  “It was also observed a peak at 2905 and 2868 cm-1 related to CH 2.”

  Gabriela Chuc-Gamboa 等 - 2021 - Antibacterial Behavior of Chitosan-Sodium Hyaluron DOI: 10.3390/app1103
• Amide confidence 1.0

  “The CH3 methyl end groups ](OH) 𝛿(OH) , whereas the combination bands + of pure, long-chain hydrocarbons produce stretching bands ](C-O) and 1st overtone amide I + amide II are visible 2905cm-1 4600cm-1 .”

  Invernizzi 等 - 2018 - Mid and Near-Infrared Reflection Spectral Database DOI: 10.1155/2018/7823248