What absorbs at 2991 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 2991 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.

가능한 작용기 할당

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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 2991 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.

이 할당의 배경이 되는 문헌

• Alkyl C-H 신뢰도 1.0

  “The two cm-1 bands at 2991 and 2948 can be attributed to the C-H bond stretching vibrations of the -CH and”

  Awad 等 - 2020 - Experimental Investigation of Methyl Methacrylate DOI: 10.3390/ma13245793
• Alkyl C-H 신뢰도 1.0

  “LLM confirmed rule peak-group candidate”

  Structural and Surface Compatibility Study of Modified Electrospun Poly(ε-caprolactone) (PCL) Composites for Skin Tissue Engineering DOI: 10.1208/s12249-016-0500-8
• Alkyl C-H 신뢰도 1.0

  “The characteristic band at 2991 cm-1 to 2976 cm-1 cm-1 cm-1 (C=C 2976 corresponds to C-H stretching vibrations, 1652 skeletal vibration), 1521”

  Complex Permittivity and Electromagnetic Interference Shielding Effectiveness of OPEFB Fiber-Polylactic Acid Filled with Reduced Graphene Oxide DOI: 10.3390/ma13204602
• Alkyl C-H 신뢰도 1.0

  “The asymmetric and symmetric C-H stretching (St.) cm1 cm1, of the methyl groups were attributed to the transmission bands at 2991 and 2943 respectively.”

  Ragab - 2022 - Improved Physical, thermal, and conductivity stren DOI: 10.21203/rs.3.rs-1514992/v1
• Alkyl C-H 신뢰도 1.0

  “The bands at 2991 and 2868 which were attributed to various C-H stretching vibrations, had opposite signs on the PC2 and PC3 loading curves.”

  Ex Vivo Vibration Spectroscopic Analysis of Colorectal Polyps for the Early Diagnosis of Colorectal Carcinoma DOI: 10.3390/diagnostics11112048
• Methyl 신뢰도 0.9

  “Explicit assignment: CH3 asymmetric stretching”

  Differentiation in MALDI-TOF MS and FTIR spectra between two pathovars of Xanthomonas oryzae DOI: 10.1016/j.saa.2014.06.056
• Methyl 신뢰도 0.9

  “Explicit assignment: 'absorption peak around 2991 ... stretching vibration peak of CH3'”

  Li 等 - 2020 - Effect of molecular weight of polyethylene glycol DOI: 10.1039/d0ra08699a
• Alkyl C-H 신뢰도 0.8

  “Text: 'strong peak at 2991.3 cm-1 (Q is assigned as the center branch) ... R(2) transition of our 5ν C-H'”

  Perez-Delgado 和 Manzanares - 2010 - Cavity Ring Down and Fourier Transform Infrared Sp DOI: 10.1021/jp105382p