13C nmr spectrum of propane C3H8 analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of alkane C13 13-C nmr doc brown's advanced organic chemistry revision notes

Advanced Organic Chemistry: Carbon-13 NMR spectrum of propane CH₃CH₂CH₃

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Interpreting and explaining the Carbon-13 NMR spectrum of propane

[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 propane [spectra page updated Mar 26th 2026 *]

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C-13 NMR spectroscopy - spectra index

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Introductory note on the 13C NMR spectrum of propane

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

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

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

13C nmr spectrum of propane C3H8 analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of alkane 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 - propane here.

Propane C₃H₈, , , ,

Interpreting the C-13 NMR spectrum of propane

As you can see from the diagram above there are 2 different ¹³C chemical shift lines in the C-13 NMR spectrum of propane indicating 2 different chemical environments of the 3 carbon atoms of propane.

CH₃CH₂CH₃

(Note the 2 different colours indicating the 2 different chemical environments of the 3 carbon atoms in propane).

¹³C chemical shifts (a) and (b) on the C-13 NMR spectrum diagram for propane.

Both chemical shifts are typical values for alkyl group carbon atoms and relatively close together.

The carbon atoms of the two 'end' methyl groups in propane are equivalent to each other i.e. identical chemical environments, so identical chemical shifts.

The carbon-13 NMR spectra provides direct evidence of 2 different ¹³C carbon atom environments for the 3 carbon atoms in the propane molecule, deduced from the presence of 3 different 13C NMR chemical shifts (ppm).

Comparing the infrared, mass, 1H NMR and 13C NMR spectra of propane, cyclopropane and propene NOTE: The images are linked to their original detailed spectral analysis pages AND can be doubled in size with touch screens to increase the definition to the original ethane and ethene image sizes.

	Comparing the infrared spectra of propane, propene and cyclopropane. Cyclopropane and propene are structural isomers of molecular formula C₃H₆. Propane and propene exemplify the infrared spectra of lower members of the alkane and alkene homologous series of C_nH_2n+2 and C_nH_2n hydrocarbon molecules where n = 3.
INFRARED SPECTRA (above): Apart from the significant differences in the fingerprint region at wavenumbers 1500 to 400 cm^-1, the most striking differences are: (i) propene shows the characteristic absorption at ~1700 cm^-1 for the C=C stretching vibrations, absent in the other two spectra, (ii) cyclopropane shows an absorption band at 2200 cm^-1, absent in the other two spectra, (iii) propane has an absorption band at ~750 cm^-1, absent in the other two spectra.

	Comparing the mass spectra of propane, propene and cyclopropane. Cyclopropane and propene are structural isomers of molecular formula C₃H₆. Propane and propene exemplify the mass spectra of lower members of the alkane and alkene homologous series of C_nH_2n+2 and C_nH_2n hydrocarbon molecules where n = 3.
MASS SPECTRA (above): All three hydrocarbons show some similarities in their mass spectra e.g. m/z ions 26 to 28 for [C₂H_x]⁺ (x = 2 to 4) and m/z 14 and 15 ions - but these are found in most aliphatic hydrocarbon spectra. The molecular ion peaks will be the same for the isomeric propene and cyclopropane (m/z 42) but that of propane will be 2 mass units higher at m/z 44. The base ion peak m/z values are all different, propane 29, propene 41 and cyclopropane 42.

	Comparing the 1H proton NMR spectra of propane, propene and cyclopropane. Cyclopropane and propene are structural isomers of molecular formula C₃H₆. Propane and propene exemplify the 1H proton NMR spectra of lower members of the alkane and alkene homologous series of C_nH_2n+2 and C_nH_2n hydrocarbon molecules where n = 3.
1H NMR SPECTRA (above): The 1H NMR spectra of all three molecules give different proton ratios i.e. propane 3:1 (actually 6:2 in the molecule), propene 2:1:3 (spectrum and molecule) and cyclopropane just a singlet for the six protons, so all three can be distinguished from each other by their ¹H NMR spectra..

	Comparing the carbon-13 NMR spectra of propane, propene and cyclopropane. Cyclopropane and propene are structural isomers of molecular formula C₃H₆. Propane and propene exemplify the carbon-13 NMR spectra of lower members of the alkane and alkene homologous series of C_nH_2n+2 and C_nH_2n hydrocarbon molecules where n = 3.
13C NMR SPECTRA (above): The 13C NMR spectra of the three molecules show different numbers of carbon-13 chemical environments i.e propane 2, propene 3 and cyclopropane only 1, so all three could be distinguished from each other.

Key words & phrases: C3H8 Interpreting the C-13 NMR spectra of propane C3H8 CH3CH2CH3 C-13 nmr spectrum of propane, understanding the carbon-13 nmr spectrum of propane, explaining the line pattern in the high resolution C-13 nmr spectra of propane, revising the C-13 nmr spectrum of propane, ppm chemical shifts of the C-13 nmr spectrum of propane, how to construct the diagram of the C-13 nmr spectrum of propane, how to analyse the chemical shifts in the carbon-13 NMR spectrum of propane deducing the chemical environment of all the carbon atoms in propane examining the c13 nmr spectrum of propane analysing the 13-c nmr spectrum of propane how do you sketch and interpret the C-13 NMR spectrum of propane interpreting interpretation of the C-13 NMR spectrum of propane assignment of chemical shifts in the 13C NMR spectrum of propane type alkane Molecular structure diagram of the carbon-13 NMR diagram for the 13C NMR spectrum of propane. Deducing the number of different chemical environments of the carbon atoms in the propane molecule from the 13C chemical shifts in the carbon-13 NMR spectrum of propane. Revision notes on the carbon-13 NMR spectrum of propane. Matching and deducing the structure of the propane molecule from its 13C NMR spectrum. How do you interpret the chemical shifts of the C-13 NMR spectrum of propane How to interpret the C-13 NMR spectrum of propane Explanatory diagram of the 13C C-13 carbon-13 NMR spectrum of the number of different carbon atom environments in the propane molecule from its carbon-13 NMR spectrum to help work out the molecular structure of the propane molecule? The uses and distinctive features of the carbon-13 NMR spectrum of the propane molecule explained. What do the number and values of the chemical shifts from the c-13 carbon-13 NMR spectrum tell us about the propane molecule? explaining the decoupled carbon-13 NMR spectrum of propane with a detailed interpretation diagram of all the C-13 chemical shifts and intensities

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The chemistry of ALKANES revision notes INDEX

The infrared spectrum of propane

The mass spectrum of propane

The H-1 NMR spectrum of propane

C-13 NMR spectroscopy index

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