Advanced Organic Chemistry: Carbon-13 NMR spectrum of 2-methylbutane

Interpreting the Carbon-13 NMR spectrum of 2-methylbutane

Doc Brown's Chemistry Advanced Level Pre-University Chemistry Revision Study Notes for UK IB KS5 A/AS GCE advanced A level organic chemistry students US K12 grade 11 grade 12 organic chemistry courses involving molecular spectroscopy analysing C-13 NMR spectra of 2-methylbutane

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C-13 NMR spectroscopy - spectra index

See also comparing the infrared, mass, 1H NMR and 13C NMR spectra of the 3 alkane isomers of C5H12

C-13 nmr spectrum of 2-methylbutane analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of 2-methylbutane 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 shifts, called chemical shifts, depend on the individual (electronic) chemical environment of the 13C atoms in an organic molecule - 2-methylbutane here.

2-methylbutane C5H12 alkanes structure and naming (c) doc b , alkanes structure and naming (c) doc b , alkanes structure and naming (c) doc b

For more see The molecular structure and naming of alkanes

Interpreting the C-13 NMR spectrum of 2-methylbutane

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

(CH3)2CHCH2CH3

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

Two of the carbon atoms have the same chemical shift a, so are equivalent to each other in the 2-methylbutane molecule, i.e. they are present in identical chemical environments.

The carbon-13 NMR spectra a provides direct evidence of 4 different 13C carbon atom environments in the 2-methylbutane molecule from 4 different chemical shifts (ppm).

Note the left-hand pair of carbon atoms of the methyl groups are in identical 13C chemical environments - plane of symmetry about the CH group.

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 CnH2n+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 CnH2n+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 [C2Hx]+ (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 CnH2n+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 CnH2n+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: isopentane methylbutane Interpreting the C-13 NMR spectra of 2-methylbutane, C-13 nmr spectrum of 2-methylbutane, understanding the carbon-13 nmr spectrum of 2-methylbutane, explaining the line pattern in the high resolution C-13 nmr spectra of 2-methylbutane, revising the C-13 nmr spectrum of 2-methylbutane, ppm chemical shifts of the C-13 nmr spectrum of 2-methylbutane, how to construct the diagram of the C-13 nmr spectrum of 2-methylbutane, how to analyse the chemical shifts in the carbon-13 NMR spectrum of 2-methylbutane deducing the chemical environment of all the carbon atoms in 2-methylbutane examining the c13 nmr spectrum of  2-methylbutane analysing the 13-c nmr spectrum of 2-methylbutane how do you sketch and interpret the C-13 NMR spectrum of 2-methylbutane isopentane methylbutane Molecular structure diagram of the carbon-13 NMR diagram for the 13C NMR spectrum of 2-methylbutane. Deducing the number of different chemical environments of the carbon atoms in the 2-methylbutane molecule from the 13C chemical shifts in the carbon-13 NMR spectrum of 2-methylbutane. Revision notes on the carbon-13 NMR spectrum of 2-methylbutane. Matching and deducing the structure of the 2-methylbutane molecule from its 13C NMR spectrum. Carbon-13 NMR spectroscopy of type, 13C NMR spectra of 2-methylbutane, an isomer of molecular formula C5H12 How do you interpret the chemical shifts of the C-13 NMR spectrum of 2-methylbutane How to interpret the C-13 NMR spectrum of 2-methylbutane Explanatory diagram of the 13C C-13 carbon-13 NMR spectrum of the  number of different carbon atom environments in the 2-methylbutane molecule from its carbon-13 NMR spectrum to help work out the molecular structure of the 2-methylbutane molecule? The uses and distinctive features of the carbon-13 NMR spectrum of the 2-methylbutane molecule explained. What do the number and values of the chemical shifts from the c-13 carbon-13 NMR spectrum tell us about the 2-methylbutane molecule? explaining the decoupled carbon-13 NMR spectrum of 2-methylbutane  with a detailed diagram of all the C-13 chemical shifts and intensities


Links associated with 2-methylbutane

The chemistry of ALKANES revision notes INDEX

The infrared spectrum for 2-methylbutane

The mass spectrum for 2-methylbutane

The H-1 NMR spectrum for 2-methylbutane

C-13 NMR spectroscopy index

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