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Interpreting the infrared
spectrum of 2-iodobutane
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 2-iodobutane
See also
comparison of the infrared, mass, 1H NMR and 13C NMR
spectra of the four isomers of C4H9I
Spectra obtained from a liquid film of 2-iodobutane. The right-hand part of the of the
infrared spectrum of 2-iodobutane, wavenumbers
~1500 to 400
cm-1 is considered the fingerprint region for the
identification of 2-iodobutane and most organic compounds. It is due to a unique set
of complex overlapping vibrations of the atoms of the molecule of
2-iodobutane.
2-iodobutane
(sec-butyl iodide), C4H9I,
CH3-CHI-CH2-CH3
Interpretation of
the infrared spectrum of 2-iodobutane
The most prominent infrared absorption lines of
2-iodobutane
For 2-iodobutane, the C-H stretching vibration absorptions
peak at
wavenumbers ~2845 to
2975 cm-1.
C-H bending/deformation vibrations absorption bands
peaking at wavenumbers ~1365 to 1470
cm-1.
These two sets of absorption bands are typical
of most alkyl structures that you see in compounds like
2-iodobutane.
C-C-C skeletal vibrations from the CH3-CH-CH2-CH2
grouping occur at wavenumbers ~1140 to 1255 cm-1 and 750
to 720 cm-1.
Characteristic groups of C-I stretching vibration
absorptions occur at
wavenumbers ~600 to 500 cm-1 that you expect in
2-iodobutane.
The absence of other specific functional group bands
will show that a particular functional group is absent from the
2-iodobutane
molecular
structure.
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Comparing the infrared, mass, 1H NMR and 13C NMR
spectra of the 4 halogenoalkane isomers of C4H9I
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 1-iodobutane,
2-iodobutane, 1-iodo-2-methylpropane and 2-iodo-2-methylpropane
image sizes. These four molecules
are structural isomers of molecular formula C4H9I
and
exemplify the infrared, mass, 1H NMR and 13C NMR spectra of lower
aliphatic halogenoalkanes (haloalkanes, alkyl halides,
iodoalkanes, alkyl iodides). |
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INFRARED SPECTRA
(above):
Apart from the significant differences in the fingerprint region at
wavenumbers 1500 to 400 cm-1, there are no other
great striking differences, but each could be identified from
its infrared spectrum. |
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MASS SPECTRA (above):
All four give the parent molecular ion of m/z 184, but it is
only a relatively tiny peak for 2-iodo-2-methylpropane. All four
give the base ion peak of m/z 57. All four give prominent peaks
for m/z ions 29 and 41 and all give a tiny peak from an ionised
iodine atom at m/z 127. They look quite similar to me and lack a
clear fingerprint fragmentation pattern. |
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1H NMR SPECTRA (above): The 1H NMR spectra of
all three molecules give different proton ratios i.e.1-iodobutane
four peaks 3:2:2:2, 2-iodobutane four peaks 3:3:2:1,
1-iodo-2-methylpropane three peaks 6:2:1 and
2-iodo-2-methylpropane one peak '1' (effectively no ratio
involved), so all four molecular structures can be distinguished from each other by their
1H NMR spectra proton ratios, numbers of peaks and (n+1)
rule splitting patterns. |
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13C NMR SPECTRA
(above): The
13C NMR spectra of the four molecules show various numbers of
carbon-13 chemical environments i.e 1-iodobutane and
2-iodobutane show four 13C NMR resonances,
1-iodo-2-methylpropane three 13C NMR resonances and
2-iodo-2-methylpropane only two 13C resonances. Therefore
1-iodo-2-methylpropane and 2-iodo-2-methylpropane can be
distinguished from the other three by their number of resonances
in their 13C NMR spectra, but 1-iodobutane and 2-iodobutane
cannot be distinguished from each other from their number of 13C
NMR resonance lines - other data would be required. |
Key words & phrases:
isomer
of molecular formula C4H9I CH3CHICH2CH3 CH3CH2CHICH3 image and diagram explaining the infrared spectrum
of 2-iodobutane, complete infrared absorption spectrum of 2-iodobutane, comparative spectra of
2-iodobutane, prominent peaks/troughs for identifying functional groups in the infrared spectrum of
2-iodobutane,
important wavenumber values in cm-1 for peaks/troughs in the infrared spectrum
of 2-iodobutane, revision of infrared spectroscopy of 2-iodobutane, fingerprint region analysis of
2-iodobutane, how to identify 2-iodobutane from its infrared spectrum, identifying organic
compounds like 2-iodobutane from their infrared spectrum,
how to analyse the absorption bands in the infrared spectrum of 2-iodobutane detection of functional groups in the
2-iodobutane molecule example of the infrared spectrum of a
molecule like 2-iodobutane with a
functional group
interpreting interpretation of the infrared spectrum of 2-iodobutane shows presence
of functional group
haloalkane halogenoalkane alkyl iodide sec-butyl iodide
Diagram of absorption of wavenumber
peaks in the infrared spectrum of 2-iodobutane. Characteristic peak wavenumbers in the infrared
spectrum of 2-iodobutane. Finger print identification pattern using the infrared
spectrum of 2-iodobutane. Revision notes on the infrared spectrum of
2-iodobutane. Matching
and deducing the structure of the 2-iodobutane molecule from its infrared
spectrum. Infrared spectroscopy of aliphatic halogenoalkanes iodoalkanes, infrared spectra of
2-iodobutane, an isomer of molecular formula C4H9I
Links associated with 2-iodobutane
The chemistry of HALOGENOALKANES (haloalkanes)
revision notes INDEX
The mass spectrum of 2-iodobutane
(sec-butyl iodide)
The H-1
NMR spectrum of 2-iodobutane (sec-butyl iodide)
The
C-13 NMR spectrum of 2-iodobutane (sec-butyl iodide)
Infrared spectroscopy index
ALL SPECTROSCOPY INDEXES
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