Advanced Organic Chemistry: Infrared spectrum of 2-methylpropan-1-ol (CH3)2CHCH2OH

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Interpreting the infrared spectrum of 2-methylpropan-1-ol (isobutyl alcohol)

[Author ©  Dr WP Brown PhD: Doc Brown's advanced level organic chemistry exam revision notes suitable for students of UK A level chemistry courses & US K12 grade 11, grade 12 and AP honors chemistry courses: Molecular spectroscopy - analysing the infrared spectrum of 2-methylpropan-1-ol [updated October 16th 2025]

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 Infrared spectroscopy - spectra index

Introductory note on the infrared spectrum of 2-methylpropan-1-ol

Students and teachers please note my explanation of the infrared spectrum of 2-methylpropan-1-ol is designed for advanced, but pre-university, chemistry courses.

Based in the infrared spectrum diagram for 2-methylpropan-1-ol, only some of the most prominent peaks for particular bond vibrations are discussed, particularly if 2-methylpropan-1-ol has a functional group with a particular characteristic wavenumber peak.

The infrared spectrum of 2-methylpropan-1-ol is unique and the whole, or selected wavenumbers, can be used to fingerprint its identity, sometimes analysing a mixture containing 2-methylpropan-1-ol or following its change of concentration in a reaction.

infrared spectrum of 2-methylpropan-1-ol C4H10O (CH3)2CHCH2OH wavenumbers cm-1 functional group detection fingerprint pattern identification of isobutyl alcohol doc brown's advanced organic chemistry revision notes 

Spectra obtained from a liquid film of 2-methylpropan-1-ol. The right-hand part of the of the infrared spectrum of 2-methylpropan-1-ol, wavenumbers ~1500 to 400 cm-1 is considered the fingerprint region for the identification of 2-methylpropan-1-ol and most organic compounds. It is due to a unique set of complex overlapping vibrations of the atoms of the molecule of 2-methylpropan-1-ol.

2-methylpropan-1-ol  C4H10O  (CH3)2CHCH2OH alcohols and ether structure and naming (c) doc b    alcohols and ether structure and naming (c) doc b    alcohols and ether structure and naming (c) doc b

The molecular structure and naming of aliphatic alcohols and ethers

Interpretation of the infrared spectrum of 2-methylpropan-1-ol

The most prominent infrared absorption lines of 2-methylpropan-1-ol

The most characteristic absorption is the broad O-H stretching vibration band at wavenumbers ~3500 to 3230 cm-1, the breadth is caused by hydrogen bonding interactions, common to all hydrogen bonded molecules with a hydroxyl group e.g. alcohols and carboxylic acids.

infrared spectrum of ethanol diagram of intermolecular hydrogen bonding forces between liquid alcohol molecules doc brown A level organic chemistry revision notes R-O–Hδ+llll:Oδ–-R ... etc.

C-H stretching vibration absorption occurs ~2900 cm-1, wavenumbers common to any molecule with alkyl groups like 2-methylpropan-1-ol.

C-C-C skeletal vibrations show absorptions at wavenumbers ~1175 to 1140 cm-1 and 840 to 790 cm-1 for a -C(CH3)2 grouping.

There are C-O stretching vibration and C-H deformation vibration absorption bands of wavenumbers ~1350 to 1030 cm-1, common to aliphatic alcohols

The absence of other specific functional group bands will show that a particular functional group is absent from the 2-methylpropan-1-ol molecular structure.

Summary of the infrared spectrum of 2-methylpropan-1-ol (isobutyl alcohol)

The IR spectrum of 2-methylpropan-1-ol (isobutyl alcohol) features a broad O–H stretch around 3300 cm⁻¹, sharp C–H stretches near 2950 cm⁻¹, and C–O stretch near 1050 cm⁻¹.

These peaks confirm the presence of an alcohol functional group and a saturated hydrocarbon backbone.

Key IR Absorptions of 2-Methylpropan-1-ol

Wavenumber (cm⁻¹) Bond Vibration Assignment
~3300 (broad) O–H stretch Strong, broad peak due to hydrogen bonding
~2950–2850 C–H stretch (alkyl) Sharp peaks from methyl and methylene groups
~1465 CH2 bending Medium intensity, scissoring vibration
~1375 CH3 bending Umbrella mode, diagnostic for methyl groups
~1050–1000 C–O stretch Sharp peak from alcohol group

Source: NIST Chemistry WebBook

Common Misconceptions about infrared spectra like that of 2-methylpropan-1-ol

  • Confusing O–H stretch with N–H or C–H: The O–H stretch is broad and intense due to hydrogen bonding, unlike sharper N–H or C–H stretches.
  • Overlooking the C–O stretch: Students often miss the C–O peak near 1050 cm⁻¹, which confirms the alcohol group.
  • Assuming all alcohols have identical spectra: Hydrogen bonding varies with structure, affecting O–H peak shape and position.

Exam Revision Tips for questions involving infrared spectra like that of 2-methylpropan-1-ol

These align with AQA, Edexcel, OCR, WJEC, CCEA, CIE, IB, and US AP Chemistry syllabi:

  • Focus on functional group regions:
    • O–H stretch: ~3200–3600 cm⁻¹ (broad)
    • C–O stretch: ~1000–1300 cm⁻¹
    • C–H stretch: ~2850–2960 cm⁻¹
  • Use IR to confirm alcohol presence: Look for both O–H and C–O peaks.
  • Compare with similar compounds: Practice distinguishing alcohols from carboxylic acids (which also have O–H but with C=O near 1700 cm⁻¹).
  • Link structure to spectrum: Understand how branching affects hydrogen bonding and peak intensity.
  • Combine with MS and NMR: Exams may ask for multi-technique analysis.

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Links associated with 2-methylpropan-1-ol

The mass spectrum of 2-methylpropan-1-ol

The H-1 NMR spectrum of 2-methylpropan-1-ol

The C-13 NMR spectrum of 2-methylpropan-1-ol

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