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Interpreting
13C NMR spectrum: 2-bromo-2-methylpropane
(tert-butyl bromide)
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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 C-13 carbon-13 NMR spectra of 2-bromo-2-methylpropane
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C-13
NMR spectroscopy - spectra index
See also
comparing
infrared, mass, 1H NMR & 13C NMR spectra of 4 halogenoalkane isomers of C4H9Br
TMS is the acronym for tetramethylsilane, formula Si(CH3)4,
whose 13C atoms are arbitrarily given a chemical shift of 0.0
ppm. This is the 'standard' in 13C NMR spectroscopy and all other
13C resonances, called chemical shifts, are measured with
respect to the TMS, and depend on the
individual (electronic) chemical environment of the 13C atoms in
an organic molecule - 2-bromo-2-methylpropane here.
2-bromo-2-methylpropane (tert-butyl bromide),
C4H9Br,
(CH3)3C-Br
Interpreting the C-13 NMR spectrum of 2-bromo-2-methylpropane
As you can see from the diagram above there are
2 different chemical shift lines in the C-13 NMR spectrum of
2-bromo-2-methylpropane
indicating 2 different chemical environments of the 4 carbon
atoms of 2-bromo-2-methylpropane.
(CH3)3C-Br
(Note the 2 different colours indicating the
2 different chemical environments of the 4 carbon atoms in
2-bromo-2-methylpropane).
13C chemical shifts (a) to (b) on the C-13 NMR
spectrum diagram for 2-bromo-2-methylpropane.
(a) (CH3)3C-Br
: 13C NMR chemical shift of 36.4 ppm for the three
equivalent
carbon atoms of the methyl groups due to the symmetry of the
2-bromo-2-methylpropane molecule.
(b) (CH3)3C-Br
: 13C NMR chemical shift of 62.5 ppm for the
carbon atom attached to the bromine atom (and methyl groups).
The carbon-13 NMR spectra provides direct evidence of
2 different carbon atom environments for the 4 carbon atoms in the
2-bromo-2-methylpropane molecule,
deduced from the presence of 2 different 13C NMR chemical
shifts (ppm).
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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 (CH3)3CBr Interpreting the C-13 NMR spectra of
2-bromo-2-methylpropane, 13C nmr spectrum of 2-bromo-2-methylpropane, understanding the carbon-13 nmr spectrum of
2-bromo-2-methylpropane,
explaining the line pattern in the high resolution C-13 nmr spectra of
2-bromo-2-methylpropane,
revising the C-13 nmr spectrum of 2-bromo-2-methylpropane, ppm chemical shifts of the C-13 nmr
spectrum of 2-bromo-2-methylpropane, how to construct the diagram of the C-13 nmr spectrum of
2-bromo-2-methylpropane,
how to analyse the chemical shifts in the carbon-13 NMR spectrum of
2-bromo-2-methylpropane deducing
the chemical environment of all the carbon atoms in 2-bromo-2-methylpropane examining the c13 nmr
spectrum of 2-bromo-2-methylpropane analysing the 13C nmr spectrum of
2-bromo-2-methylpropane how do you sketch and interpret the C-13 NMR spectrum
of 2-bromo-2-methylpropane interpreting interpretation of the C-13 NMR spectrum
of 2-bromo-2-methylpropane
assignment of chemical shifts in the 13C
NMR spectrum of 2-bromo-2-methylpropane
tert-butyl bromide alkyl halide
haloalkane alkyl bromide bromoalkane
Molecular structure diagram of the
carbon-13 NMR diagram for the 13C NMR spectrum of 2-bromo-2-methylpropane. Deducing the number
of different chemical environments of the carbon atoms in the
2-bromo-2-methylpropane molecule
from the 13C chemical shifts in the carbon-13 NMR spectrum of
2-bromo-2-methylpropane. Revision
notes on the carbon-13 NMR spectrum of 2-bromo-2-methylpropane. Matching and deducing the
structure of the 2-bromo-2-methylpropane molecule from its 13C NMR spectrum.
Carbon-13 NMR spectroscopy of
halogenoalkanes bromoalkanes alkyl bromides,
13C NMR spectra of 2-bromo-2-methylpropane, an isomer of molecular formula
C4H9Br
Links associated
with 2-bromo-2-methylpropane
The chemistry of HALOGENOALKANES (haloalkanes)
revision notes INDEX
The
infrared spectrum of 2-bromo-2-methylpropane
(tert-butyl bromide)
The
mass spectrum of 2-bromo-2-methylpropane
(tert-butyl bromide)
The H-1 NMR spectrum of
2-bromo-2-methylpropane
(tert-butyl bromide)
C-13
NMR spectroscopy index
ALL SPECTROSCOPY INDEXES
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