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Interpreting the infrared
spectrum of propan-2-ol
(2-propanol)
CH3CH(OH)CH3
(re-edit)
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 propan-2-ol
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Links associated with propan-2-ol
Infrared spectroscopy - spectra index
See also
comparing the infrared, mass, 1H NMR and 13C NMR
spectra of the 3 isomers of C3H8O
Spectra obtained from a liquid film of propan-2-ol. The right-hand part of the of the
infrared spectrum of propan-2-ol, wavenumbers
~1500 to 400
cm-1 is considered the fingerprint region for the
identification of propan-2-ol and most organic compounds. It is due to a unique set
of complex overlapping vibrations of the atoms of the molecule of
propan-2-ol.
Propan-2-ol, C3H8O,
,
,
 ,
Interpretation of
the infrared spectrum of propan-2-ol (2-propanol,
isopropyl alcohol)
The most prominent infrared absorption lines of
propan-2-ol
The most characteristic absorption is the broad O-H
stretching vibration band at wavenumbers ~3500 to 3230 cm-1,
the breadth is caused by hydrogen bonding interactions, common to
all hydrogen bonded molecules with a hydroxyl group e.g. alcohols
and carboxylic acids.
R-O–Hδ+llllδ–:O-R
... etc.
C-H stretching vibration absorption occurs ~2900 cm-1,
wavenumbers common to any molecule with alkyl groups.
C-C-C skeletal vibrations show absorptions at
wavenumbers ~1175 to 1140 cm-1 and 840 to 790 cm-1
for a -C(CH3)2 grouping in propan-2-ol.
There are C-O stretching vibration and C-H
deformation vibration absorption bands of wavenumbers ~1350 to 1030 cm-1, common to
aliphatic alcohols like propan-2-ol.
The absence of other specific functional group bands
will show that particular functional group is absent from the
propan-2-ol
molecular
structure.
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Comparing the infrared, mass, 1H NMR and 13C NMR
spectra of the 3 isomers of C3H8O
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 propan-1-ol,
propan-2-ol and methoxyethane image sizes. |
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I wasn't able to obtain an infrared
spectrum for methoxyethane, so I've added the infrared spectrum
of ethoxyethane to enable a few comparisons with two aliphatic
alcohols
Comparing the
infrared
spectra of
propan-1-ol,
propan-2-ol and
methoxyethane
Propan-1-ol,
propan-2-ol and methoxyethane
are structural isomers of molecular formula C3H8O
Propan-1-ol,
propan-2-ol and methoxyethane
exemplify infrared spectra of the lower members of the homologous series
of aliphatic alcohols and ethers |
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INFRARED SPECTRA
(above): There are, as expected, differences in the fingerprint region at
wavenumbers 1500 to 400 cm-1, but most absorptions
for all three molecules are the various C-O and the many C-H
vibrational modes. However, there is one characteristic distinguishing
absorption only present in the infrared spectra of alcohols, but
not in ethers, that is the broad O-H stretching vibration
peaking at ~3350 cm-1. There is also another broad
absorption band (origin?) peaking at ~650 cm-1 in the
alcohol spectra, but not in the ether spectra. |
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Comparing the
mass
spectra of
propan-1-ol,
propan-2-ol and
methoxyethane
Propan-1-ol,
propan-2-ol and methoxyethane
are structural isomers of molecular formula C3H8O
Propan-1-ol,
propan-2-ol and methoxyethane
exemplify the mass spectra of the lower members of the homologous series
of aliphatic alcohols and ethers |
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MASS SPECTRA (above):
The base ion peaks are m/z 45 for propan-2-ol and methoxyethane,
but that of propan-1-ol is m/z 31. Many of the fragmentation
ions are common to all three spectra. The m/z 45 ion is peak is
much smaller in the propan-1-ol spectrum compared to the other
two. |
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Comparing the
1H proton NMR
spectra of
propan-1-ol,
propan-2-ol and
methoxyethane
Propan-1-ol,
propan-2-ol and methoxyethane
are structural isomers of molecular formula C3H8O
Propan-1-ol,
propan-2-ol and methoxyethane exemplify the 1H proton NMR spectra of
the lower members of the homologous series of aliphatic alcohols and
ethers |
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1H NMR SPECTRA (above): The 1H NMR spectra of
all three molecules give different integrated proton ratios for the
different 1H chemical environments i.e. the proton
ratios are as follows: propan-1-ol
3:2:2:1; propan-2-ol 6:1:1 and methoxyethane
3:2:3. Therefore, all three can be distinguished by their
1H NMR spectra. |
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Comparing the
carbon-13 NMR
spectra of
propan-1-ol,
propan-2-ol and
methoxyethane
Propan-1-ol,
propan-2-ol and methoxyethane
are structural isomers of molecular formula C3H8O
Propan-1-ol,
propan-2-ol and methoxyethane exemplify the carbon-13 NMR spectra of
members of the lower members of the homologous series of aliphatic
alcohols and ethers |
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13C NMR SPECTRA
(above): The
13C NMR spectra of propan-1-ol and methoxyethane show
three different 13C NMR chemical shifts, but
propan-2-ol can be distinguished from the other two by
exhibiting only two chemical shift lines. You would need other
spectral data to distinguish propan-1-ol and methoxyethane. |
Key words & phrases: CH3CHOHCH3 2-propanol isopropyl alcohol image and diagram explaining the infrared spectrum
of propan-2-ol, complete infrared absorption spectrum of propan-2-ol, comparative spectra of
propan-2-ol, prominent peaks/troughs for identifying functional groups in the infrared spectrum of
propan-2-ol,
important wavenumber values in cm-1 for peaks/troughs in the infrared spectrum
of propan-2-ol, revision of infrared spectroscopy of propan-2-ol, fingerprint region analysis of
propan-2-ol, how to identify propan-2-ol from its infrared spectrum, identifying organic
compounds like propan-2-ol from their infrared spectrum,
how to analyse the absorption bands in the infrared spectrum of propan-2-ol detection of
alcohol hydroxyl functional groups in the propan-2-ol molecule example of the infrared spectrum of a
molecule like propan-2-ol with a functional group ? 2-propanol isopropyl alcohol isomer of molecular formula
C3H8O Diagram of absorption of wavenumber
peaks in the infrared spectrum of propan-2-ol 2-propanol. Characteristic peak wavenumbers in the infrared
spectrum of propan-2-ol 2-propanol. Finger print identification pattern using the infrared
spectrum of propan-2-ol 2-propanol. Revision notes on the infrared spectrum of
propan-2-ol 2-propanol. Matching
and deducing the structure of the propan-2-ol 2-propanol molecule from its infrared
spectrum. Infrared spectroscopy of aliphatic secondary alcohols, infrared spectra of
propan-2-ol 2-propanol, an isomer of molecular formula C3H8O Explanatory diagram of the infrared spectrum of the propan-2-ol 2-propanol molecule in terms of its molecular structure. Listing data of the prominent main wavenumber peaks troughs in the infrared spectrum of propan-2-ol 2-propanol. How to explain the infrared spectrum of propan-2-ol 2-propanol. Use of the infrared spectrum of propan-2-ol 2-propanol, identification of propan-2-ol 2-propanol from its infrared spectrum - fingerprint wavenumber pattern to identify the propan-2-ol 2-propanol molecule. The uses of the infrared spectrum of the propan-2-ol 2-propanol molecule. The distinctive features of the infrared spectrum of the propan-2-ol 2-propanol molecule explained. explaining the peaks-trough of the transmittance of the infrared spectrum of propan-2-ol 2-propanol what does the infrared spectrum tell you about the structure and properties of the propan-2-ol 2-propanol molecule?
Links associated
with propan-2-ol
The chemistry of ALCOHOLS
revision notes INDEX
The mass spectrum of Propan-2-ol (2-propanol,
isopropyl alcohol)
The H-1 NMR spectrum of Propan-2-ol (2-propanol,
isopropyl alcohol)
The C-13 NMR spectrum
of Propan-2-ol (2-propanol,
isopropyl alcohol)
Infrared spectroscopy index
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