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The H-1
hydrogen-1 (proton) NMR spectrum of propane
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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 H-1 NMR spectra of propane
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H-1 proton NMR spectroscopy -
spectra index
See also
comparing the infrared, mass, 1H
NMR and 13C NMR
spectra of propane, cyclopropane and propene
TMS is the acronym for tetramethylsilane, formula Si(CH3)4,
whose protons are arbitrarily given a chemical shift of 0.0 ppm.
This is the 'standard' in 1H NMR spectroscopy and all
other proton shifts, called chemical shifts, depend on the
individual (electronic) chemical environment of the hydrogen atoms
in an organic molecule - propane here.
In terms of spin-spin coupling from the possible proton magnetic
orientations, for propane I
have only considered the interactions of
non-equivalent protons on adjacent carbon atoms
e.g. -CH2-CH3
protons.
The chemical shifts quoted in ppm on the diagram of
the H-1 NMR spectrum of propane represent the peaks of the intensity of
the chemical shifts of (which are often groups of split lines at
high resolution) AND the relative integrated areas under the peaks
gives you the ratio of protons in the different chemical
environments of the propane molecule.
Propane C3H8,
 ,
,
,
Interpreting the
H-1 NMR spectrum of
propane (dissolved in CDCl3)
For relatively simple molecules, the low
resolution H-1 NMR spectrum of propane is a good starting point
(low resolution diagram above).
The hydrogen atoms (protons) of propane occupy 2
different chemical environments so that the low resolution NMR
spectra should show 2 peaks of different H-1 NMR chemical shifts (diagram above for
propane).
CH3CH2CH3
Note the ratio 6:2 = 3:1 of the two colours of the protons
in the two chemically different environments
Although there are 8 hydrogen atoms in the molecule,
there only 2 possible chemical
environments for the hydrogen atoms in propane molecule.
The overall proton ratio 3:1 observed, corresponds with
the structural formula of propane.
The high resolution H-1 NMR spectrum
of propane
All low and high resolution spectra of propane
show two groups of protons and in the ratio 3:1 expected from the
formula of propane.
The ppm quoted on the diagram represent the peak
of resonance intensity for a particular proton group in the
molecule of propane - since the peak' is at the apex of a band of
H-1 NMR resonances due to spin - spin coupling field splitting effects - see high resolution
notes on propane below.
So, using the chemical shifts and applying the
n+1 rule
to propane
Chemical shift (a) 0.90 ppm, the two groups of CH3
protons: CH3CH2CH3
This proton resonance split by the CH2
protons into a 1:2:1 triplet (n+1 = 3)
Evidence for the presence of a CH2 group
in the molecule of propane
Chemical shift (b) 1.34 ppm, the one group of CH2
protons: CH3CH2CH3
The central CH2 group protons
are split on either side by a group of CH3
protons (6 protons in total) into a 1:6:15:20:15:6:1
septet (n+1 = 7)
Evidence for the presence of a two CH3 groups
separated by a carbon atom with at least one proton on it
in the molecule of propane i.e. CH3-CHx-CH3
grouping.
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Number of protons 1H
causing splitting |
Splitting pattern produced from the
n+1 rule and the theoretical ratio of line intensities |
| 0
means no splitting |
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1 |
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| 1
creates a doublet |
|
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|
1 |
|
1 |
|
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| 2
creates a triplet |
|
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|
1 |
|
2 |
|
1 |
|
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| 3
creates a quartet |
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|
1 |
|
3 |
|
3 |
|
1 |
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| 4
creates a quintet |
|
|
1 |
|
4 |
|
6 |
|
4 |
|
1 |
|
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| 5
creates a sextet |
|
1 |
|
5 |
|
10 |
|
10 |
|
5 |
|
1 |
|
| 6
creates a septet |
1 |
|
6 |
|
15 |
|
20 |
|
15 |
|
6 |
|
1 |
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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. |
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 |
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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 CnH2n+2 and CnH2n
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. |
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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 CnH2n+2 and CnH2n
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 [C2Hx]+
(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. |
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 |
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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 CnH2n+2 and CnH2n
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.. |
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 |
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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 CnH2n+2 and CnH2n
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: Interpreting the proton H-1 NMR spectra of propane
C3H8 CH3CH2CH3, low resolution & high resolution proton
nmr spectra of propane, H-1 nmr spectrum of propane, understanding the
hydrogen-1 nmr spectrum of propane, explaining the line splitting patterns in the
high resolution H-1 nmr spectra of propane, revising the H-1 nmr spectrum of
propane,
proton nmr of propane, ppm chemical shifts of the H-1 nmr spectrum of propane,
explaining and analyzing spin spin line splitting in the H-1 nmr spectrum, how
to construct the diagram of the H-1 nmr spectrum of propane, how to work out the
number of chemically different protons in the structure of the propane organic
molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR
spectrum of propane using the n+1 rule to explain the spin - spin coupling ine
splitting in the proton nmr spectrum of propane deducing the nature of the protons
from the chemical shifts ppm in the H-1 nmr spectrum of propane
examining the 1H nmr spectrum of propane analysing the 1-H nmr spectrum of
propane how do you sketch and interpret the H-1 NMR spectrum of propane Molecular structure diagram of the
proton NMR diagram for the 1H NMR spectrum of propane. The proton ratio in the
1H NMR spectrum of propane. Deducing the number of different chemical
environments of the protons in the propane molecule from the 1H chemical shifts
in the hydrogen-1 NMR spectrum of propane. Analysing the high resolution 1H NMR
spectrum of propane. Analysing the low resolution 1H NMR spectrum of propane. You
may need to know the relative molecular mass of propane to deduce the molecular
formula from the proton ratio of the 1H NMR spectrum of propane. Revision notes
on the proton NMR spectrum of propane. Matching and deducing the structure of
the propane molecule from its hydrogen-1 NMR spectrum.
Links associated
with propane
The chemistry of ALKANES
revision notes INDEX
The infrared
spectrum of propane
(Please
read 8 points at the top of the 1H NMR index page)
The mass
spectrum of propane
The C-13 NMR
spectrum of propane
H-1 proton NMR spectroscopy index
ALL SPECTROSCOPY INDEXES
All Advanced Organic
Chemistry Notes
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