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Interpreting the infrared
spectrum of 1-bromobutane
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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 1-bromobutane
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Infrared spectroscopy - spectra index
See also
comparing
infrared, mass, 1H NMR & 13C NMR spectra of 4 halogenoalkane isomers of C4H9Br
Spectra obtained from a liquid film of 1-bromobutane. The right-hand part of the of the
infrared spectrum of 1-bromobutane, wavenumbers
~1500 to 400
cm-1 is considered the fingerprint region for the
identification of 1-bromobutane and most organic compounds. It is due to a unique set
of complex overlapping vibrations of the atoms of the molecule of
1-bromobutane.
1-bromobutane,
C4H9Br,
CH3CH2CH2CH2Br,
CH3-CH2-CH2-CH2-Br
Interpretation of
the infrared spectrum of 1-bromobutane
The most prominent infrared absorption lines of
1-bromobutane
C-H stretching vibration absorptions peak at
wavenumbers ~2845 to
2975 cm-1.
C-H bending/deformation vibrations absorption bands
peaking at wavenumbers ~1270 to 1470
cm-1.
C-C-C skeletal vibrations from the CH2-CH2-CH2
grouping occur at wavenumbers ~1370 to 1250 cm-1 and 840
to 790 cm-1.
These absorption bands are typical of most alkyl
structures you see in molecules like 1-bromobutane.
Characteristic groups of C-Br stretching vibration
absorptions at
wavenumbers ~550 to 750 cm-1 that you expect in
1-bromobutane.
The absence of other specific functional group bands
will show that a particular functional group is absent from the
1-bromobutane
molecular
structure.
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Comparing the infrared, mass, 1H NMR and 13C NMR
spectra of the 4 halogenoalkane isomers of C4H9Br
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-bromobutane,
2-bromobutane, 1-bromo-2-methylpropane and 2-bromo-2-methylpropane
image sizes. These four molecules
are structural isomers of molecular formula C4H9Br
and
exemplify the infrared, mass, 1H NMR and 13C NMR spectra of lower
aliphatic halogenoalkanes (haloalkanes, alkyl halides,
bromoalkanes, alkyl bromides). |
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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 ions of m/z 136 and 138, but it is
only a relatively tiny peak for 2-bromobutane and 2-bromo-2-methylpropane. All four
give the base ion peak of m/z 57. All four give prominent peaks
for m/z ions 27, 29, 39 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. There are small
differences in the relative abundances (peak heights) for pairs
of ions involving 79Br/81Br isotopes e.g.
m/z 93/95, 107/109 and 121/123. 1-bromo-2-methylpropane is the
only one of the four to have a prominent peak for the m/z 43
ion. |
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1H NMR SPECTRA
(above): The 1H NMR spectra of all four molecules give different
integrated proton ratios i.e.1-bromobutane
four peaks of ratio 3:2:2:2; 2-bromobutane four peaks of
ratio 3:3:2:1,
1-bromo-2-methylpropane three peaks of ratio 6:2:1 and
2-bromo-2-methylpropane gives just 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-bromobutane and
2-bromobutane show four 13C NMR resonances,
1-bromo-2-methylpropane three 13C NMR resonances and
2-bromo-2-methylpropane only two 13C resonances. Therefore
1-bromo-2-methylpropane and 2-bromo-2-methylpropane can be
distinguished from the other three by their number of resonances
in their 13C NMR spectra, but 1-bromobutane and 2-bromobutane
cannot be distinguished from each other from their number of 13C
NMR resonance lines - other data would be required. |
Key words & phrases:
C4H9Br
CH3CH2CH2CH2Br image and diagram explaining the infrared spectrum
of 1-bromobutane, complete infrared absorption spectrum of 1-bromobutane, comparative spectra of
1-bromobutane, prominent peaks/troughs for identifying functional groups in the infrared spectrum of
1-bromobutane,
important wavenumber values in cm-1 for peaks/troughs in the infrared spectrum
of 1-bromobutane, revision of infrared spectroscopy of 1-bromobutane, fingerprint region analysis of
1-bromobutane, how to identify 1-bromobutane from its infrared spectrum, identifying organic
compounds like 1-bromobutane from their infrared spectrum,
how to analyse the absorption bands in the infrared spectrum of 1-bromobutane detection of functional groups in the
1-bromobutane molecule example of the infrared spectrum of a
molecule like 1-bromobutane with a
functional group
interpreting interpretation of the infrared spectrum of 1-bromobutane shows presence
of n-butyl
iodide alkyl halide
functional group haloalkane halogenoalkane
bromoalkane Diagram of absorption of wavenumber
peaks in the infrared spectrum of 1-bromobutane. Characteristic peak wavenumbers in the infrared
spectrum of 1-bromobutane. Finger print identification pattern using the infrared
spectrum of 1-bromobutane. Revision notes on the infrared spectrum of
1-bromobutane. Matching
and deducing the structure of the 1-bromobutane molecule from its infrared
spectrum. Infrared spectroscopy of aliphatic halogenoalkanes bromoalkanes
alkyl bromides, infrared spectra of
1-bromobutane, an isomer of molecular formula C4H9Br
Links associated with 1-bromobutane
The chemistry of HALOGENOALKANES (haloalkanes)
revision notes INDEX
The mass spectrum of 1-bromobutane
(n-butyl bromide)
The H-1 NMR spectrum of
1-bromobutane (n-butyl bromide)
The C-13 NMR spectrum of
1-bromobutane (n-butyl bromide)
Infrared spectroscopy index
ALL SPECTROSCOPY INDEXES
All Advanced Organic
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