What absorbs at 2906 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 2906 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 2906 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

  “0.626±0.007 0.623±0.006 0.60 *** CH3 asymmetric stretching 2944.54±0.17 2944.59±0.29 0.81 0.719±0.030 0.074±0.036 CH2 asymmetric stretching 2905.65±0.58 2905.45±0.17 0.60 0.630±0.021 0.642±0.028 0.58 CH3 symmetric stretching”

  Differentiation in MALDI-TOF MS and FTIR spectra between two pathovars of Xanthomonas oryzae DOI: 10.1016/j.saa.2014.06.056
• Hydroxyl (O-H) confidence 1.0

  “In a comparison, the band peaked at 2906 cm-1 can be attributed to presence of OH groups that could be confirmed by the appearance of broad band with a maximum at 3351cm-1 cm-1 C-H stretching in dextran [32,33], since such band was not obse”

  Development of Polymer Blend Electrolyte Membranes Based on Chitosan: Dextran with High Ion Transport Properties for EDLC Application DOI: 10.3390/ijms20133369
• Alkyl C-H confidence 1.0

  “This is convincing evidence of an increased amorphous region within at 3351cm⁻1 as shown in Figure 4c [51,52].Figure 4calso exhibits a band at 2906 cm⁻1that is related to C-H stretching [51-53].”

  Structural, Impedance and Electrochemical Characteristics of Electrical Double Layer Capacitor Devices Based on Chitosan: Dextran Biopolymer Blend Electrolytes DOI: 10.3390/polym12061411
• Alkyl C-H confidence 1.0

  “The 2906 cm-1 band corresponds to the C-H bonds, which are characteristic of organic molecules found in natural components.”

  Impact and Tensile Properties of Polyester Nanocomposites Reinforced with Conifer Fiber Cellulose Nanocrystal:A Previous Study Extension DOI: 10.3390/polym13111878
• Alkyl C-H confidence 1.0

  “cm-1 as gas phase methane at 3015 In addition, peaks are present at 2906 and a cm-1 sym shoulder at 2885 which are attributed to a methine (CH) stretching mode and the”

  Mcnab 等 - 2017 - Quantification and qualification by in-situ FTIR o DOI: 10.1016/S0926-860X(99)00160-X.
• Alkyl C-H confidence 1.0

  “LLM confirmed rule peak-group candidate”

  Preparation and Optimization of Water-Soluble Cationic Sago Starch with a High Degree of Substitution Using Response Surface Methodology DOI: 10.3390/polym12112614
• Alkyl C-H confidence 1.0

  “2937.98 C-H stretching 2906.38 C-H stretching 2872.47 =”

  Development of Flexible Plasticized Ion Conducting Polymer Blend Electrolytes Based on Polyvinyl Alcohol (PVA): Chitosan (CS) with High Ion Transport Parameters Close to Gel Based Electrolytes DOI: 10.3390/gels
• Alkyl C-H confidence 1.0

  “The peak at 2906 corresponds with the asymmetric and symmetric cm-1 stretching of -CH groups [32,36].”

  Design of Asymmetric Nanofibers-Membranes Based on Polyvinyl Alcohol and Wool-Keratin for Wound Healing Applications DOI: 10.3390/jfb12040076