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Interpreting the
H-1 hydrogen-1 (proton) NMR spectrum of propene
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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 propene
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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 resonances, called chemical shifts, are measured
with respect to the TMS, and depend on the
individual (electronic) chemical environment of the hydrogen atoms
in an organic molecule - propene here.
The chemical shifts quoted in ppm on the diagram of
the H-1 NMR spectrum of propene 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 propene molecule.
Propene,
 ,
 ,
 ,
 ,
 ,
Interpreting the
H-1 NMR spectrum of
propene
In terms of spin-spin coupling from the possible proton magnetic orientations,
for propene I
have only considered the interactions of
non-equivalent protons on adjacent carbon atoms
e.g. -CH2=CH, -CH-CH3-, protons
etc.
For relatively simple molecules, the low
resolution H-1 NMR spectrum of propene is a good starting point
(low resolution diagram above).
The 6 hydrogen atoms (protons) of propene
appear to occupy 3
different chemical environments so that the low resolution NMR
spectra should show 3 principal peaks of different H-1 NMR chemical shifts (diagram above for
propene).
CH2=CH-CH3
Note the proton ratio of 2:1:3 of the 3 colours of the
6 protons of propene
in the 3 chemically different proton environments
Chemical shifts (a)/(b) : (c) : (d) on the H-1 NMR
spectrum diagram for propene.
The high resolution 1H NMR
spectrum of propene
However, the high resolution spectra of propene
shows 4 groups of proton resonances and in the 1:1:1:3 ratio expected from the
structural
formula of propene.
The
two resonances for the protons of the end =CH2 group are very
slightly different due to these two protons experiencing slightly
different shielding field effects due to the asymmetric grouping at the
other end of the C=C bond. (It doesn't matter which way round you draw
the structure of propene!)
The ppm quoted on the diagram represent the peak
of resonance intensity for a particular proton group in the
molecule of propene - 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 propene below.
So, using the chemical shifts and applying the
n+1 rule to
propene
and make some predictions using some colour coding! (In problem
solving you work the other way round!)
For propene this is actually quite tricky and NOT what
you might expect because of the slightly different chemical shifts of
the H2C= end protons in propene, meaning they are NOT
equivalent.
Resonance
(a) and (b) 1H Chemical shift: CH2=CH-CH3
1H NMR chemical shifts of 5.00 and 4.93 ppm.
You might think that the resonance for the CH2
protons would be split into a doublet by the lone CH proton (n+1 =
2), but you can see from the higher resolution spectrum, there are
quite a few lines!
What us happening is that each CH2 proton
is split by the other proton and by the lone CH proton.
You therefore have two triplets overlapping each
other (two n+1 = 3).
Resonance
(c) 1H Chemical shift: CH2=CH-CH3
1H NMR chemical shift of 5.84 ppm.
Again, we have problems with interpretation and you
might expect the CH resonance to be split into a sextet by the
adjacent CH2 and CH3 protons on either side
(n+1 = 6).
BUT not so, the CH proton resonance is split by the
CH3 proton field but also separately by the individual CH2
protons, to give two overlapping quintets (two n+1 = 5).
Resonance
(d) 1H Chemical shift: CH2=CH-CH3
1H NMR chemical shift of 1.65 ppm.
This is split into a doublet by the adjacent CH
group proton (n+1 = 2), with no complications!
Evidence of a -CH- grouping in the molecule.
|
Number of directly adjacent protons 1H
causing splitting |
Splitting pattern produced from the
n+1 rule on spin-spin coupling 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 |
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1 |
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| 2
creates a triplet |
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1 |
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2 |
|
1 |
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| 3
creates a quartet |
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|
1 |
|
3 |
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3 |
|
1 |
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| 4
creates a quintet |
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|
1 |
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4 |
|
6 |
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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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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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 |
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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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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:
C3H6
H2C=CHCH3 CH3CH=CH2 CH2=CHCH3 Interpreting the proton H-1 NMR spectra of propene, low resolution & high resolution proton
nmr spectra of propene, H-1 nmr spectrum of propene, understanding the
hydrogen-1 nmr spectrum of propene, explaining the line splitting patterns from
spin-spin coupling in the
high resolution H-1 nmr spectra of propene, revising the H-1 nmr spectrum of
propene,
proton nmr of propene, ppm chemical shifts of the H-1 nmr spectrum of propene,
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 propene, how to work out the
number of chemically different protons in the structure of the propene organic
molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR
spectrum of propene using the n+1 rule to explain the spin - spin coupling ine
splitting in the proton nmr spectrum of propene deducing the nature of the protons
from the chemical shifts ppm in the H-1 nmr spectrum of propene
examining the 1H nmr spectrum of propene analysing the 1-H nmr spectrum of
propene
how do you sketch and interpret the H-1 NMR spectrum of propene interpreting
interpretation of the 1H proton spin-spin coupling causing line splitting in the
NMR spectrum of propene
assignment of chemical shifts in the
proton 1H NMR spectrum of propene formula explaining spin-spin coupling for line
splitting for propene alkene functional group
propylene Molecular structure diagram of the
proton NMR diagram for the 1H NMR spectrum of propene. The proton ratio in the
1H NMR spectrum of propene. Deducing the number of different chemical
environments of the protons in the propene molecule from the 1H chemical shifts
in the hydrogen-1 NMR spectrum of propene. Analysing the high resolution 1H NMR
spectrum of propene. Analysing the low resolution 1H NMR spectrum of propene. You
may need to know the relative molecular mass of propene to deduce the molecular
formula from the proton ratio of the 1H NMR spectrum of propene. Revision notes
on the proton NMR spectrum of propene. Matching and deducing the structure of
the propene molecule from its hydrogen-1 NMR spectrum.
Links associated
with propene
The chemistry of ALKENES
revision notes INDEX
The infrared spectrum of
propene ('propylene')
The
mass spectrum of propene ('propylene')
The C-13 NMR spectrum of
propene ('propylene')
H-1 proton NMR spectroscopy index
(Please
read 8 points at the top of the 1H NMR index page)
ALL SPECTROSCOPY INDEXES
All Advanced Organic
Chemistry Notes
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