Advanced Organic Chemistry: The 13C NMR spectrum of butan-2-ol  (2-butanol) CH3CH2CH(OH)CH3

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Interpreting and explaining the carbon-13 C13 NMR spectrum of butan-2-ol

CH3CH(OH)CH2CH3 (2-butanol, sec-butanol, sec-butyl alcohol)

[Author ©  Dr Phil Brown PhD: Doc Brown's advanced level pre-university/college organic chemistry exam revision notes suitable for students of UK A level chemistry courses & US K12 grade 11, grade 12 & AP honors chemistry courses: Molecular spectroscopy of butan-2-ol (2-butanol) [spectrum page updated Mar 3rd 2026 *]

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Introductory note on the 13C NMR spectrum of butan-2-ol

Students and teachers please note that my explanation of the carbon-13 NMR spectrum of butan-2-ol is designed for advanced, but pre-university, chemistry courses.

The description does not involve the chemical shift δ spin-spin coupling effects for butan-2-ol and the relative size of the carbon-13 NMR shifts does not give the ratio of the carbon atoms in the different non-equivalent chemical environments of the butan-2-ol molecule.

The most common solvent used for investigating the C13 NMR spectrum of compounds like butan-2-ol, is CDCl3 and other deuterated solvents.

C4H10O CH3CH(OH)CH2CH3 C-13 nmr spectrum of butan-2-ol analysis of chemical shifts ppm interpretation of 13C chemical shifts ppm of 2-butanol sec-butyl alcohol C13 13-C nmr doc brown's advanced organic chemistry revision notes 

TMS is the acronym for tetramethylsilane, formula Si(CH3)4, whose 13C atoms are arbitrarily given a chemical shift of 0.0 ppm. This is the 'standard' in 13C NMR spectroscopy and all other 13C resonances, called chemical shifts, are measured with respect to the TMS, and depend on the individual (electronic) chemical environment of the 13C atoms in an organic molecule - butan-2-ol here.

Butan-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 

A secondary alcohol The molecular structure and naming of aliphatic alcohols and ethers

Interpreting the C-13 NMR spectrum of butan-2-ol (2-butanol)

As you can see from the diagram above there are 4 different chemical shift lines in the C-13 NMR spectrum of butan-2-ol indicating 4 different chemical environments of the 4 carbon atoms of butan-2-ol.

CH3CH(OH)CH2CH3

(Note the 4 different colours indicating the 4 different chemical environments of the 4 carbon atoms in butan-2-ol).

13C chemical shifts (a) to (d) on the C-13 NMR spectrum diagram for butan-2-ol.

(a) δ 22.8 ppm for the CH3 carbon nearest to the OH group.

(b) δ 69.3 ppm for the CH carbon nearest (attached) to the OH group.

Note the effect on the C-13 NMR shift of the very electronegative oxygen.

(c) δ 32.1 ppm for the CH2 group carbon

(d) δ 10.0 ppm for the carbon of the CH3 group farthest from OH group, the smallest chemical shift.

Note the decreasing effect on the 13C chemical shift as the carbon atom is further from the more electronegative oxygen atom in the molecule of butan-2-ol.

The carbon-13 NMR spectra provides direct evidence of 4 different carbon atom environments for the 4 carbon atoms in the butan-2-ol molecule, deduced from the presence of 4 different 13C NMR chemical shifts (ppm).

Key revision points about the 13C NMR spectrum of butan-2-ol (2-butanol)

An exam‑focused breakdown of the ¹³C NMR spectrum of butan‑2‑ol (2‑butanol), designed for advanced A level, IB, and AP Honors chemistry students:

Key Features of the 13C NMR Spectrum of Butan‑2‑ol

  • Four distinct carbon environments (C4H10O has 4 unique carbons).
  • Chemical shift range: ~10–70 ppm (no carbonyl, so no signals >160 ppm).
  • Most deshielded carbon: The secondary carbon bonded to OH (~65–70 ppm).
  • Methylene carbon: ~25–35 ppm.
  • Methyl carbons: ~10–20 ppm, with slightly different shifts depending on position.
  • No signals in aromatic or carbonyl regions — useful diagnostic absence.

Table of 13C Chemical Shifts and Origins for the 13C NMR spectrum of butan-2-ol (2-butanol)

δ (ppm) range Carbon type Origin / Explanation
~65–70, 69.3 CH–OH Secondary carbon bonded to OH, deshielded by electronegative oxygen
~25–35, 32.1 CH2 Methylene carbon adjacent to CH–OH and terminal CH3
~18–20, 22.8 CH3 (attached to CH–OH) Methyl group bonded to the alcohol carbon
~10–12, 10.0 CH3 (terminal) Methyl group at end of chain, most shielded

Spectra data source https://sdbs.db.aist.go.jp/Disclaimer.aspx for 13C δ ppm

Common Student Misconceptions for the 13C NMR spectrum of butan-2-ol (2-butanol)

  • Expecting more than 4 signals: Students sometimes forget symmetry reduces the number of distinct carbons.
  • Confusing chemical shift ranges: They may expect alcohol carbons to appear in the carbonyl region (>160 ppm). In reality, alcohol carbons are much lower (~50–70 ppm).
  • Overlooking subtle differences between methyl carbons: Both CH3 groups give signals, but at slightly different ppm values.
  • Assuming OH proton affects 13C directly: The OH group influences the adjacent carbon’s shift, but the OH itself does not appear in 13C NMR.

Exam Revision Tips for the 13C NMR spectrum of butan-2-ol (2-butanol)

  • Count distinct carbons: Always check molecular symmetry to predict the number of signals.
  • Identify the deshielded carbon (~65–70 ppm): This is diagnostic of the C–OH carbon.
  • Check for absence of carbonyl signals: No peaks >160 ppm confirms it’s not a ketone, aldehyde, or carboxylic acid.
  • Compare methyl shifts: Terminal CH3 (~10 ppm) versus CH3 attached to C–OH (~18 ppm).
  • Exam technique: When asked to assign signals, state ppm, carbon type, and reasoning (e.g., “Signal at ~68 ppm corresponds to the secondary carbon bonded to OH, deshielded by oxygen”).
  • Cross‑board consistency: All exam boards (AQA, Edexcel, OCR, WJEC, CCEA, CIE, IB, AP) expect recognition of the number of signals, approximate ranges, and diagnostic deshielding effects.

Final Guidance for the 13C NMR spectrum of butan-2-ol (2-butanol)

For A level and AP exams, focus on:

  • Four signals only (distinct carbons).
  • Deshielded C–OH carbon at ~65–70 ppm.
  • Two methyl carbons at ~10–20 ppm.
  • Absence of carbonyl peaks.

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Links associated with butan-2-ol

The infrared spectrum of butan-2-ol (sec-butyl alcohol)

The mass spectrum of butan-2-ol (sec-butyl alcohol)

The H-1 NMR spectrum of butan-2-ol (sec-butyl alcohol)

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Website content © Dr Phil Brown 2000+. All copyrights reserved on revision notes, images, quizzes, worksheets etc. Copying of Doc Brown's pre-university/college advanced level chemistry website material is NOT permitted. Exam revision summaries & references to chemistry course specifications are unofficial. These organic chemistry revision notes on the spectroscopy of butan-2-ol (2-butanol) - its 13C NMR spectrum are suitable for use of pre-university students studying AQA advanced level chemistry, Edexcel advanced level chemistry, OCR advanced level chemistry, IB advanced level chemistry, WJEC (Eduqas) advanced level chemistry, CIE Cambridge advanced level chemistry, US grade 11-12 AP honors chemistry courses and they will also prove useful to 1st year undergraduate students of chemistry.

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