Advanced Organic Chemistry: The 13C NMR spectrum of phenol C6H5OH

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Interpreting and explaining the Carbon-13 NMR spectrum of phenol C6H5OH

[Author © Dr Phil 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 13C NMR spectra of phenol [spectra page updated April 4th 2026 *]

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 C-13 NMR spectroscopy - spectra index

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Introductory note on the 13C NMR spectrum of phenol

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

The description does not involve the chemical shift δ spin-spin coupling effects for phenol 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 phenol molecule.

The most common solvent used for investigating the 13C NMR spectrum of compounds like phenol, is CDCl3 and other deuterated solvents.

13C nmr spectrum of phenol C6H6O C6H5OH analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of phenol 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 - phenol here.

Phenol,  C6H6O,  C6H5OH, (c) doc b ,  (c) doc b

The molecular structure and naming of aromatic compounds

Interpreting the C-13 NMR spectrum of phenol

As you can see from the diagram above there are 4 different 13C chemical shift lines in the C-13 NMR spectrum of phenol indicating 4 different chemical environments of the 6 carbon atoms of phenol.

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

aromatic benzene ring carbon atom positions in phenol 13C NMR spectroscopy

Numbering of benzene ring carbon atoms.  Ring positions in monosubstituted benzene compounds. Note that C2 = C6 and C3 = C5 for 13C nmr shifts, this is an important point of symmetry for the 13c chemical shifts for these protons, so only three 13C shifts for the benzene ring carbon atoms.

As a consequence of the symmetry of phenol:

Resonance13C  (b) is for the two chemically equivalent carbon atoms 2 and 6.

Resonance13C  (c) is for the two chemically equivalent carbon atoms 3 and 5.

Carbon atom 1, resonance (a) and carbon atom 4, resonance (d), resonance are not equivalent to each other or to any other carbon atoms in the benzene ring.

The carbon-13 NMR spectra provides direct evidence of 4 different carbon atom environments for the 6 carbon atoms in the phenol molecule, deduced from the presence of 4 different 13C NMR chemical shifts (ppm).

Key points about the 13C NMR Spectrum of Phenol

Phenol (C6H5OH) has six carbons, but due to symmetry in the monosubstituted benzene ring, some carbons are equivalent:

  • C2 = C6 (ortho carbons) → equivalent by symmetry.
  • C3 = C5 (meta carbons) → equivalent by symmetry.
  • C4 (para carbon) → unique.
  • C1 (ipso carbon, bonded to OH) → unique, strongly deshielded.

So in total, phenol shows 4 distinct 13C signals, not 6.

Table of 13C Chemical Shifts for Phenol

δ (ppm) Range Carbon Origin Notes
~150–155, 155.0 ppm C1 Ipso carbon bonded to OH Strongly deshielded by electronegative oxygen
~125–130, 115.5 ppm C2 & C6 Ortho carbons Equivalent pair
~115–120, 129.8 ppm C3 & C5 Meta carbons Equivalent pair
~125–130 C4 Para carbon Unique environment

Sources: NIST WebBook (Phenol ¹³C NMR), ChemicalBook spectrum data, Organic Chemistry Data repositories.

Common Misconceptions

  • Thinking phenol has 6 signals: Students often forget symmetry reduces the number of distinct carbons.
  • Confusing the ipso carbon with a carbonyl: The δ ~150 ppm signal is due to C–OH, not a C=O group.
  • Expecting integration to matter in ¹³C NMR: Unlike ¹H NMR, signal intensity does not directly reflect number of carbons.

Exam Revision Tips

  • Always count symmetry: For monosubstituted benzenes, check which carbons are equivalent.
  • Identify the ipso carbon (~150 ppm): This is diagnostic of phenols.
  • Compare with benzene: Benzene has 1 signal (δ ~128 ppm); phenol has 4 signals due to substitution.
  • Exam technique:
    1. State number of distinct signals (4).
    2. Assign ipso carbon.
    3. Group equivalent carbons (C2=C6, C3=C5).
    4. Relate chemical shifts to electronegativity and aromatic environment.

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Links associated with phenol

The H-1 NMR spectrum of phenol

The C-13 NMR spectrum of phenol

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The infrared spectrum of phenol

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