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Carbon-13 NMR spectrum of Pentane
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 pentane
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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
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,
 ,
,
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)
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 chemical shifts are observed
in C-13 NMR spectrum.
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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. |
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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 |
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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. |
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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 |
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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. |
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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 |
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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. |
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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 |
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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
Associated links
The chemistry of ALKANES
revision notes INDEX
The infrared spectrum of pentane
The mass spectrum of Pentane
The H-1 NMR spectrum of pentane
C-13
NMR spectroscopy index
ALL SPECTROSCOPY INDEXES
All Advanced Organic
Chemistry Notes
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