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Interpreting the infrared
spectrum of cyclopropane
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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 infrared spectra of cyclopropane
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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 cyclopropane. The right-hand part of the of the
infrared spectrum of cyclopropane, wavenumbers
~1500 to 400
cm-1 is considered the fingerprint region for the
identification of cyclopropane and most organic compounds. It is due to a unique set
of complex overlapping vibrations of the atoms of the molecule of
cyclopropane.
Cyclopropane C3H6,
 ,
Interpretation of
the infrared spectrum of cyclopropane
The most prominent infrared absorption lines of
cyclopropane
C-H stretching vibrations peak at wavenumbers ~3080
to 3040 cm-1 for cyclopropane.
Not sure what vibrations cause the sharp band at
~2200 cm-1.
-CH2- deformation vibrations peak at
wavenumbers 1480 to 1440 cm-1 for cyclopropane.
Cyclopropane shows
-CH2- skeletal vibration absorption bands peaking
at wavenumbers 1020 to 1000 cm-1.
Cyclopropane shows many absorption bands in common with aliphatic
hydrocarbon molecules.
The absence of other specific functional group bands
will show that a particular functional group is absent from the
cyclopropane
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 image and diagram explaining the infrared spectrum
of cyclopropane, complete infrared absorption spectrum of cyclopropane, comparative spectra of
cyclopropane, prominent peaks/troughs for identifying functional groups in the infrared spectrum of
cyclopropane,
important wavenumber values in cm-1 for peaks/troughs in the infrared spectrum
of cyclopropane, revision of infrared spectroscopy of cyclopropane, fingerprint region analysis of
cyclopropane, how to identify cyclopropane from its infrared spectrum, identifying organic
compounds like cyclopropane from their infrared spectrum,
how to analyse the absorption bands in the infrared spectrum of cyclopropane detection of functional groups in the
cyclopropane molecule example of the infrared spectrum of a
molecule like cyclopropane with a ?
functional group
interpreting interpretation of the infrared spectrum of cyclopropane shows presence
of cycloalkane functional group
Diagram of absorption of wavenumber
peaks in the infrared spectrum of cyclopropane. Characteristic peak wavenumbers in the infrared
spectrum of cyclopropane. Finger print identification pattern using the infrared
spectrum of cyclopropane. Revision notes on the infrared spectrum of
cyclopropane. Matching
and deducing the structure of the cyclopropane molecule from its infrared
spectrum.
Links associated with cyclopropane
The chemistry of ALKANES
revision notes INDEX
The mass
spectrum of cyclopropane
The H-1 NMR of cyclopropane
The
C-13 NMR spectrum of cyclopropane
Infrared spectroscopy index
ALL SPECTROSCOPY INDEXES
All Advanced Organic
Chemistry Notes
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