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Interpreting the
Carbon-13 NMR spectrum of 2-bromobutane
(sec-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 NMR spectra of 2-bromobutane
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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-bromobutane here.
2-bromobutane, C4H9Br,
CH3CHBrCH2CH3,
CH3-CH(Br)-CH2-CH3
Secondary haloalkane/halogenoalkane and
old names: sec-butyl bromide, sec-butyl bromide (secondary alkyl
halide)
Interpreting the C-13 NMR spectrum of 2-bromobutane
As you can see from the diagram above there are
4 different chemical shift lines in the C-13 NMR spectrum of
2-bromobutane
indicating 4 different chemical environments of the 4 carbon
atoms of 2-bromobutane.
CH3-CHBr-CH2-CH3
(Note the 4 different colours indicating the
4 different chemical environments of the 4 carbon atoms in
2-bromobutane).
13C chemical shifts (a) to (d) on the C-13 NMR
spectrum diagram for 2-bromobutane.
(a) 13C NMR chemical shift of 26.1
ppm for the left methyl carbon atom:
(b) 13C NMR chemical shift of 53.4
ppm for the CH carbon atom:
(c) 13C NMR chemical shift of 34.3
ppm for the CH2 carbon atom:
(d) 13C NMR chemical shift of 12.2
ppm for the right methyl carbon atom:
Note the decreasing effect on the 13C chemical shift as the
carbon atom is further from the more electronegative oxygen and
nitrogen bromine chlorine atom in 2-bromobutane.
The carbon-13 NMR spectra provides direct evidence of
4 different carbon atom environments for the 4 carbon atoms in the
2-bromobutane molecule,
deduced from the presence of 4 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 CH3CHBrCH2CH3 CH3CH2CHBrCH3 Interpreting the C-13 NMR spectra of
2-bromobutane, C-13 nmr spectrum of 2-bromobutane, understanding the
carbon-13 nmr spectrum of 2-bromobutane, explaining the line pattern in the high
resolution C-13 nmr spectra of 2-bromobutane, revising the C-13 nmr spectrum of
2-bromobutane, ppm
chemical shifts of the C-13 nmr spectrum of 2-bromobutane, how to construct the diagram of
the C-13 nmr spectrum of 2-bromobutane, how to analyse the chemical shifts in the
carbon-13 NMR spectrum of 2-bromobutane deducing the chemical environment of all the
carbon atoms in 2-bromobutane examining the c13 nmr spectrum of
2-bromobutane analysing the
13-c nmr spectrum of 2-bromobutane how do you sketch and interpret the C-13 NMR spectrum
of 2-bromobutane interpreting interpretation of the C-13 NMR spectrum of
2-bromobutane
assignment of chemical shifts in the 13C
NMR spectrum of 2-bromobutane
sec-butyl bromide sec-butyl bromide
alkyl bromide alkyl halide haloalkane halogenoalkane
Molecular structure diagram of the
carbon-13 NMR diagram for the 13C NMR spectrum of 2-bromobutane (sec-butyl
bromide). Deducing the number
of different chemical environments of the carbon atoms in the 2-bromobutane
(sec-butyl bromide) molecule
from the 13C chemical shifts in the carbon-13 NMR spectrum of 2-bromobutane
(sec-butyl bromide). Revision
notes on the carbon-13 NMR spectrum of 2-bromobutane (sec-butyl bromide). Matching and deducing the
structure of the 2-bromobutane (sec-butyl bromide) molecule from its 13C NMR spectrum.
Links associated
with 2-bromobutane
The chemistry of HALOGENOALKANES (haloalkanes)
revision notes INDEX
The infrared spectrum of 2-bromobutane
(sec-butyl bromide)
The mass
spectrum of 2-bromobutane (sec-butyl bromide)
The H-1
NMR spectrum of 2-bromobutane (sec-butyl bromide)
C-13
NMR spectroscopy index
ALL SPECTROSCOPY INDEXES
All Advanced Organic
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