C-13 nmr spectrum of pentane analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of pentane diagram doc brown's advanced organic chemistry revision notes

Advanced Organic Chemistry: Carbon-13 13C NMR spectrum of Pentane CH₃(CH₂)₃CH₃

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Interpreting & explaining the Carbon-13 NMR spectrum of Pentane

[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 pentane [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 pentane

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

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

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

C-13 nmr spectrum of pentane analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of pentane diagram 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 - pentane here.

Pentane C₅H₁₂, , , an alkane

For more see The molecular structure and naming of alkanes

Interpreting the C-13 NMR spectrum of Pentane

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

CH₃CH₂CH₂CH₂CH₃

(Note the 3 different colours of the carbon atoms in pentane, indicating the three different ¹³C chemical environments)

All ¹³C NMR chemical shifts (a) to (c) are typical values for alkyl group carbon atoms and relatively close together.

Although there are five carbon atoms in the molecule, pentane is a symmetrical molecule with only three possible ¹³C chemical environments for the 5 carbon atoms, so three ¹³C chemical shifts are observed in C-13 NMR spectrum.

Comparing the infrared, mass, 1H NMR and 13C NMR spectra of the 3 alkane isomers of C₅H₁₂ 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 pentane, 2-methylbutane and 2,2-dimethylpropane image sizes.

	Comparing the infrared spectra of pentane, 2-methylbutane and 2,2-dimethylpropane Pentane, 2-methylbutane and 2,2-dimethylpropane are structural isomers of molecular formula C₅H₁₂ Pentane, 2-methylbutane and 2,2-dimethylpropane exemplify infrared spectra of the alkane homologous series C_nH_2n+2 hydrocarbon molecules, where n = 5
INFRARED SPECTRA (above): There are, as expected, differences in the fingerprint region at wavenumbers 1500 to 400 cm^-1, but there is no specific infrared absorption band for a functional group. The infrared spectra of pentane and 2-methylbutane seem very similar, but that of 2,2-dimethylpropane seems much simpler.

	Comparing the mass spectra of pentane, 2-methylbutane and 2,2-dimethylpropane Pentane, 2-methylbutane and 2,2-dimethylpropane are structural isomers of molecular formula C₅H₁₂ Pentane, 2-methylbutane and 2,2-dimethylpropane exemplify the mass spectra of the alkane series C_nH_2n+2 hydrocarbon molecules, where n = 5
MASS SPECTRA (above): All three hydrocarbons show some similarities in their mass spectra e.g. m/z ions 27 to 29 for [C₂H_x]⁺ (x = 2 and 4). The molecular ion peaks will be the same for all three isomers (m/z 72), but it is very tiny for 2,2-dimethypropane. The pattern ratios for m/z 39 to 43 are similar for pentane and 2-methylbutane, but m/z 42 and 43 ions are almost absent from the 2,2-dimethylpropane spectrum. The base peak ion for pentane is m/z 43, but for 2-methylbutane and 2,2-dimethylpropane it is m/z 57.

	Comparing the 1H proton NMR spectra of pentane, 2-methylbutane and 2,2-dimethylpropane Pentane, 2-methylbutane and 2,2-dimethylpropane are structural isomers of molecular formula C₅H₁₂ Pentane, 2-methylbutane and 2,2-dimethylpropane exemplify the 1H proton NMR spectra of the alkane homologous series C_nH_2n+2 hydrocarbon molecules where, n = 5
1H NMR SPECTRA (above): The 1H NMR spectra of all three molecules give different proton ratios for the different ¹H chemical environments i.e. pentane's proton ratio is 3:2:1 (from 6:4:2 H's in the molecule). 2-methylbutane's proton ratio is 6:1:2:3 and 2,2-dimethylpropane's doesn't have a proton ratio, all hydrogen atoms are equivalent. This means all three isomeric C₅H₁₂ hydrocarbons can be distinguished from their 1H NMR spectra.

	Comparing the carbon-13 NMR spectra of pentane, 2-methylbutane and 2,2-dimethylpropane Pentane, 2-methylbutane and 2,2-dimethylpropane are structural isomers of molecular formula C₅H₁₂ Pentane, 2-methylbutane and 2,2-dimethylpropane exemplify the carbon-13 NMR spectra of members of the alkane homologous series C_nH_2n+2 hydrocarbon molecules, where n = 5
13C NMR SPECTRA (above): The ¹³C NMR spectra of the three molecules show different numbers of carbon-13 chemical environments i.e different numbers of 13C NMR resonance lines. So, pentane gives three ¹³C chemical shifts, 2-methylbutane four and 2,2-dimethylpropane two. This means all three isomeric C₅H₁₂ hydrocarbons can be distinguished from their 13C NMR spectra.

Key words & phrases: Interpreting the C-13 NMR spectra of pentane, C-13 nmr spectrum of pentane, understanding the carbon-13 nmr spectrum of pentane, explaining the line pattern in the high resolution C-13 nmr spectra of pentane, revising the C-13 nmr spectrum of pentane, ppm chemical shifts of the C-13 nmr spectrum of pentane, how to construct the diagram of the C-13 nmr spectrum of pentane Molecular structure diagram of the carbon-13 NMR diagram for the 13C NMR spectrum of pentane. Deducing the number of different chemical environments of the carbon atoms in the pentane molecule from the 13C chemical shifts in the carbon-13 NMR spectrum of pentane. Revision notes on the carbon-13 NMR spectrum of pentane. Matching and deducing the structure of the pentane molecule from its 13C NMR spectrum. Carbon-13 NMR spectroscopy of alkane, 13C NMR spectra of pentane, an isomer of molecular formula C5H12 How do you interpret the chemical shifts of the C-13 NMR spectrum of pentane How to interpret the C-13 NMR spectrum of pentane Explanatory diagram of the 13C C-13 carbon-13 NMR spectrum of the number of different carbon atom environments in the pentane molecule from its carbon-13 NMR spectrum to help work out the molecular structure of the pentane molecule? The uses and distinctive features of the carbon-13 NMR spectrum of the pentane molecule explained. What do the number and values of the chemical shifts from the c-13 carbon-13 NMR spectrum tell us about the pentane molecule? explaining the decoupled carbon-13 NMR spectrum of pentane with a detailed interpretation diagram of all the C-13 chemical shifts and intensities

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The infrared spectrum of pentane

The mass spectrum of Pentane

The H-1 NMR spectrum of pentane

C-13 NMR spectroscopy index

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