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Interpreting1H 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 H-1 proton NMR spectra of 2-bromo-2-methylpropane
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H-1 proton 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 protons are arbitrarily given a chemical shift of 0.0 ppm.
This is the 'standard' in 1H NMR spectroscopy and all
other proton resonances, called chemical shifts, are measured
with respect to the TMS, and depend on the
individual (electronic) chemical environment of the hydrogen atoms
in an organic molecule - 2-bromo-2-methylpropane here.
The chemical shifts quoted in ppm on the diagram of
the H-1 NMR spectrum of 2-bromo-2-methylpropane represent the peaks of the intensity of
the chemical shifts of (which are often groups of split lines at
high resolution) AND the relative integrated areas under the peaks
gives you the ratio of protons in the different chemical
environments of the 2-bromo-2-methylpropane molecule.
2-bromo-2-methylpropane
(tert-butyl bromide), C4H9Br,
(CH3)3C-Br
Interpreting the
H-1 NMR spectrum of
2-bromo-2-methylpropane
In terms of spin-spin coupling from the possible proton magnetic orientations,
for 2-bromo-2-methylpropane there
no interactions of non-equivalent protons on adjacent carbon atoms
e.g. no -CH2-CH3
or -CH2-CH2-, proton situations
etc.
Due to the symmetry of the
2-bromo-2-methylpropnae molecule, all 9 protons occupy the
same chemical environment and as a consequence there no
splitting of the 1H NMR resonance.
Therefore both high or low resolution spectra will only show
a single singlet 1H NMR resonance line.
(CH3)3C-Br
One colour for the
9 protons of 2-bromo-2-methylpropane, as all the hydrogen atoms
are
in the same chemical environment.
Chemical shift (a) of 1.80 ppm on the H-1 NMR
spectrum diagram for 2-bromo-2-methylpropane above.
No need for the
n+1 rule,
life couldn't be simpler!
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Number of directly adjacent protons 1H
causing splitting |
Splitting pattern produced from the
n+1 rule on spin-spin coupling and the theoretical ratio of line intensities |
| 0
means no splitting |
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1 |
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| 1
creates a doublet |
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1 |
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1 |
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| 2
creates a triplet |
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1 |
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2 |
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1 |
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| 3
creates a quartet |
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1 |
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3 |
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3 |
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1 |
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| 4
creates a quintet |
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1 |
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4 |
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6 |
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4 |
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1 |
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| 5
creates a sextet |
|
1 |
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5 |
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10 |
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10 |
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5 |
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1 |
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| 6
creates a septet |
1 |
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6 |
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15 |
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20 |
|
15 |
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6 |
|
1 |
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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 proton H-1 NMR spectra of 2-bromo-2-methylpropane, low resolution & high
resolution proton nmr spectra of 2-bromo-2-methylpropane, H-1 nmr spectrum of
2-bromo-2-methylpropane, understanding the
hydrogen-1 nmr spectrum of 2-bromo-2-methylpropane, explaining the line splitting patterns from
spin-spin coupling in the high resolution H-1 nmr spectra of
2-bromo-2-methylpropane, revising
the H-1 nmr spectrum of 2-bromo-2-methylpropane, proton nmr of
2-bromo-2-methylpropane, ppm chemical shifts of the H-1
nmr spectrum of 2-bromo-2-methylpropane, explaining and analyzing spin spin line splitting in the
H-1 nmr spectrum, how to construct the diagram of the 1H nmr spectrum of
2-bromo-2-methylpropane, how to work out the
number of chemically different protons in the structure of the
2-bromo-2-methylpropane organic
molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR
spectrum of 2-bromo-2-methylpropane using the n+1 rule to explain the spin - spin coupling ine
splitting in the proton nmr spectrum of 2-bromo-2-methylpropane deducing the nature of the protons
from the chemical shifts ppm in the H-1 nmr spectrum of 2-bromo-2-methylpropane
examining the 1H nmr spectrum of 2-bromo-2-methylpropane analysing the 1H nmr spectrum of
2-bromo-2-methylpropane
how do you sketch and interpret the H-1 NMR spectrum of 2-bromo-2-methylpropane
interpreting interpretation of the 1H proton spin-spin coupling causing line
splitting in the NMR spectrum of 2-bromo-2-methylpropane
assignment of chemical shifts in the
proton 1H NMR spectrum of 2-bromo-2-methylpropane formula explaining spin-spin
coupling for line splitting for 2-bromo-2-methylpropane tert-butyl bromide alkyl halide
haloalkane alkyl bromide bromoalkane
functional group
Molecular structure diagram of the
proton NMR diagram for the 1H NMR spectrum of 2-bromo-2-methylpropane. The proton ratio in the
1H NMR spectrum of 2-bromo-2-methylpropane. Deducing the number of different chemical
environments of the protons in the 2-bromo-2-methylpropane molecule from the 1H chemical shifts
in the hydrogen-1 NMR spectrum of 2-bromo-2-methylpropane. Analysing the high resolution 1H NMR
spectrum of 2-bromo-2-methylpropane. Analysing the low resolution 1H NMR spectrum of
2-bromo-2-methylpropane. You
may need to know the relative molecular mass of 2-bromo-2-methylpropane to deduce the molecular
formula from the proton ratio of the 1H NMR spectrum of
2-bromo-2-methylpropane. Revision notes
on the proton NMR spectrum of 2-bromo-2-methylpropane. Matching and deducing the structure of
the 2-bromo-2-methylpropane molecule from its hydrogen-1 NMR spectrum.
Proton NMR spectroscopy of
halogenoalkanes bromoalkanes alkyl bromides,
1H 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
C-13 NMR spectrum of 2-bromo-2-methylpropane
(tert-butyl bromide)
H-1 proton NMR spectroscopy index
(Please
read 8 points at the top of the 1H NMR index page)
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