Advanced Organic Chemistry: Infrared spectrum of 2-methylpropan-2-ol (CH3)3COH

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Interpreting the infrared spectrum of 2-methylpropan-2-ol (tert-butyl 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-2-ol [updated October 24th 2025]

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Infrared spectroscopy - spectra index

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

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

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

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

C4H10O (CH3)3COH infrared spectrum of 2-methylpropan-2-ol wavenumbers cm-1 functional group detection fingerprint pattern identification of tert-butyl alcohol doc brown's advanced organic chemistry revision notes 

Spectra obtained from a liquid film of 2-methylpropan-2-ol. The right-hand part of the of the infrared spectrum of 2-methylpropan-2-ol, wavenumbers ~1500 to 400 cm-1 is considered the fingerprint region for the identification of 2-methylpropan-2-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-2-ol.

2-methylpropan-2-ol   C4H10O  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-2-ol

The most prominent infrared absorption lines of 2-methylpropan-2-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.

C-C-C skeletal vibrations show absorptions at wavenumbers ~1255 to 1200 cm-1 and 750 to 720 cm-1 for a -C(CH3)3 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-2-ol molecular structure.

Key points about the infrared spectrum of 2-methylpropan-2-ol

2-Methylpropan-2-ol shows a broad O–H stretch around 3200–3600 cm⁻¹ and strong C–H stretches near 2950 cm⁻¹; absence of C=O confirms it's not a ketone or acid.

Key IR Spectrum Features of 2-Methylpropan-2-ol

2-Methylpropan-2-ol (tert-butanol) is a tertiary alcohol with the formula (CH3)3COH.

Its IR spectrum reflects characteristic functional group vibrations:

Wavenumber (cm⁻¹) Bond / Vibration Description
3200–3600 O–H stretch (alcohol) Broad, strong peak due to hydrogen bonding; hallmark of alcohols
~2950 C–H stretch (alkyl) Sharp peaks from methyl C–H stretching vibrations
~1450–1375 C–H bending (methyl groups) Medium intensity; confirms presence of multiple CH3 groups
~1050–1150 C–O stretch (alcohol) Strong, sharp peak; confirms alcohol functionality
<1500 Fingerprint region Complex pattern; useful for compound identification but not functional groups

Sources: NIST Chemistry WebBook

Common Misconceptions in Exams

  • Mistaking the O–H stretch for N–H or carboxylic acid: Alcohol O–H is broad but not as broad or intense as carboxylic acids.
  • Assuming all alcohols show identical O–H peaks: Tertiary alcohols like 2-methylpropan-2-ol may show less hydrogen bonding, slightly narrowing the peak.
  • Overinterpreting the fingerprint region: Students often try to assign peaks <1500 cm⁻¹ without sufficient data—this region is best used for comparison, not deduction.
  • Missing the absence of C=O: A key diagnostic feature—no peak near 1700 cm⁻¹ confirms it's not a ketone, aldehyde, or acid.

Exam Revision Tips

  • Use IR to confirm or eliminate functional groups: For example, absence of C=O rules out ketones and acids.
  • Compare spectra to known standards: Practice with spectra of ethanol, propan-2-ol, and carboxylic acids to distinguish O–H types.
  • Label spectra in mock exams: Annotate key peaks with bond types and wavenumbers—this builds pattern recognition.
  • Watch for distractors in MCQs: Some exams include spectra with overlapping features—focus on the most diagnostic peaks.
  • Practice with real spectra: Use NIST or exam board resources to interpret actual IR plots, not just tables.

Would you like a printable overlay comparing IR spectra of primary, secondary, and tertiary alcohols for revision?

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Links associated with 2-methylpropan-2-ol

The mass spectrum of 2-methylpropan-2-ol

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

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

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