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Interpreting the infrared
spectrum of propene
('propylene')
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 infrared spectra of propene
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Infrared spectroscopy - spectra index
See also
comparing the infrared, mass, 1H
NMR and 13C NMR
spectra of propane, cyclopropane and propene
Spectra obtained from a liquid film of propene. The right-hand part of the of the
infrared spectrum of propene, wavenumbers
~1500 to 400
cm-1 is considered the fingerprint region for the
identification of propene and most organic compounds. It is due to a unique set
of complex overlapping vibrations of the atoms of the molecule of propene.
Propene,
 ,
 ,
 ,
 ,
 ,
Interpretation of
the infrared spectrum of propene
The most prominent infrared absorption lines of propene
There are prominent bands of C-H stretching
vibration absorptions peaking at wavenumbers ~3095 to 3010 cm-1,
and also 995 to 905 cm-1, associated with the C-H bond in
a RCH=CH2 grouping e.g. as in propene.
Overlapping with the above, are prominent bands due
to C-H stretching vibration absorptions peak at wavenumbers ~2975 to
2860 cm-1, typical of molecules with a methyl alkyl group.
There is a very strong characteristic absorption
for C=C stretching vibrations, peaking at wavenumbers 1645 to 1640 cm-1,
typical of an alkene like propene.
Around wavenumbers ~1470 to 1370 cm-1 are
absorptions dues to C-H deformation vibrations of the C-CH3
grouping in propene.
The absence of other specific functional group bands
will show that a particular functional group is absent from the
propene
molecular
structure.
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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. |
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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. |
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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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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. |
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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. |
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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 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 image and diagram explaining the infrared spectrum
of propene, complete infrared absorption spectrum of propene, comparative spectra of
propene, prominent peaks/troughs for identifying functional groups in the infrared spectrum of
propene,
important wavenumber values in cm-1 for peaks/troughs in the infrared spectrum
of propene, revision of infrared spectroscopy of propene, fingerprint region analysis of
propene, how to identify propene from its infrared spectrum, identifying organic
compounds like propene from their infrared spectrum,
how to analyse the absorption bands in the infrared spectrum of propene detection of
alkene functional groups in the propene molecule example of the infrared spectrum of a
molecule like propene with a alkene
functional group
interpreting interpretation of the infrared spectrum of propene shows presence
of alkene functional group
alkene functional group
propylene Diagram of absorption of wavenumber
peaks in the infrared spectrum of propene. Characteristic peak wavenumbers in the infrared
spectrum of propene. Finger print identification pattern using the infrared
spectrum of propene. Revision notes on the infrared spectrum of propene. Matching
and deducing the structure of the propene molecule from its infrared
spectrum.
Links associated with propene
The chemistry of ALKENES
revision notes INDEX
The
mass spectrum of propene ('propylene')
The H-1 NMR spectrum of
propene ('propylene')
The C-13 NMR spectrum of
propene ('propylene')
Infrared spectroscopy index
ALL SPECTROSCOPY INDEXES
All Advanced Organic
Chemistry Notes
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