Advanced Organic Chemistry: Carbon-13 NMR spectrum of (1-methylethyl)benzene (cumene)

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Interpreting and explaining the Carbon-13 NMR spectrum of (1-methylethyl)benzene, 2-phenylpropane (cumene, isopropylbenzene)

[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 analysis of cumene [spectra page updated Mar 22nd 2026 *]

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 C-13 NMR spectroscopy - spectra index

Introductory note on the 13C NMR spectrum of cumene

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

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

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

C9H12 C-13 nmr spectrum of (1-methylethyl)benzene (cumene) analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of 2-phenylpropane C13 13C 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 shifts, called chemical shifts, depend on the individual (electronic) chemical environment of the 13C atoms in an organic molecule - (1-methylethyl)benzene (cumene) here.

 (1-methylethyl)benzene, 2-phenylpropane, C9H12, , (cumene, isopropylbenzene)

The molecular structure and naming of aromatic compounds

Interpreting the C-13 NMR spectrum of (1-methylethyl)benzene (cumene)

As you can see from the diagram above there are 6 different 13C chemical shift lines in the C-13 NMR spectrum of (1-methylethyl)benzene (cumene) indicating 6 different chemical environments of the carbon atoms.

On the C-13 NMR spectrum diagram for (1-methylethyl)benzene you can see chemical shifts (a) to (d) are for the benzene ring carbon atoms and two chemical shifts (e) and (f) for the side-chain carbon atoms of the alkyl group CH(CH3)2.

In the 13-C NMR spectrum of cumene, the aromatic ring carbons tend to be bunched together at higher chemical shifts than the alkyl group carbon atoms, which are also bunched together at lower 13C NMR chemical shift vales.

This arises from two bunches of similar, if not identical, chemical environments:

(i) Aromatic carbon ring atoms (chemical shifts a-d) and

(ii) alkyl group carbon atoms (chemical shifts e-f). The methyl group carbon atoms are equivalent to each other.

The carbon-13 NMR spectra a provides direct evidence of 6 different carbon atom environments in the (1-methylethyl)benzene (cumene) molecule from 6 different 13C chemical shifts (ppm).

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Links associated with (1-methylethyl)benzene (cumene)

The infrared spectrum of (1-methylethyl)benzene  or  2-phenylpropane (Cumene)

The mass spectrum of (1-methylethyl)benzene or  2-phenylpropane (Cumene)

The H-1 NMR spectrum of (1-methylethyl)benzene  or  2-phenylpropane (Cumene)

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