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The H-1
hydrogen-1 (proton) NMR spectrum of bromomethane
(methyl 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 NMR spectra of bromomethane
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H-1 proton NMR spectroscopy -
spectra index
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 - bromomethane here.
The chemical shifts quoted in ppm on the diagram of
the H-1 NMR spectrum of bromomethane 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 bromomethane molecule.
Bromomethane, CH3Br
(methyl bromide)
Interpreting the
H-1 NMR spectrum of
bromomethane
There is only one 1H chemical shift observed, because there
is only one protonated carbon atom attached to three equivalent hydrogen
atoms - which cannot split each other, so all you see in the 1H NMR spectrum
of bromomethane is a single singlet resonance.
Comparing the 1H NMR chemical shift of bromomethane with
other halogen compounds
(1)
Comparing monosubstituted halogen derivatives of methane
Comparing the effect of a mono-substituent in
the methane molecule
| Compound |
fluoromethane |
chloromethane |
bromomethane |
iodomethane |
methane |
| Formula |
CH3F |
CH3Cl |
CH3Br |
CH3I |
CH4 |
| 1H chemical
shift/ppm |
4.1 |
3.05 |
2.68 |
2.16 |
0.23 |
| Pauling
electronegativity |
F
4.0 |
Cl
3.0 |
Br
2.8 |
I
2.5 |
H
2.1 |
With the increase in electronegativity of the halogen, the 1H
chemical shift for these molecules steadily increases.
(2) Comparing the
effects of increasing chlorine substitution of methane
Comparing the effect of polysubstitution of methane with
chlorine.
| Compound |
methane |
chloromethane |
dichloromethane |
trichloromethane |
tetrachloromethane |
| Formula |
CH4 |
CH3Cl |
CH2Cl2 |
CHCl3 |
CCl4 |
| 1H chemical
shift/ppm |
0.23 |
3.05 |
5.30 |
7.27 |
not
applicable |
With increase in chlorine substitution, the 1H NMR chemical
shift is increased.
Increasing the number of atoms more electronegative than
carbon or hydrogen, increases the 1H NMR chemical shift.
You would expect a similar trend for the equivalent bromine
compounds.
|
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 |
|
|
|
|
|
|
1 |
|
|
|
|
|
|
| 1
creates a doublet |
|
|
|
|
|
1 |
|
1 |
|
|
|
|
|
| 2
creates a triplet |
|
|
|
|
1 |
|
2 |
|
1 |
|
|
|
|
| 3
creates a quartet |
|
|
|
1 |
|
3 |
|
3 |
|
1 |
|
|
|
| 4
creates a quintet |
|
|
1 |
|
4 |
|
6 |
|
4 |
|
1 |
|
|
| 5
creates a sextet |
|
1 |
|
5 |
|
10 |
|
10 |
|
5 |
|
1 |
|
| 6
creates a septet |
1 |
|
6 |
|
15 |
|
20 |
|
15 |
|
6 |
|
1 |
Key words & phrases:
formula
Interpreting the proton H-1 NMR spectra of bromomethane, low resolution & high resolution proton
nmr spectra of bromomethane, H-1 nmr spectrum of bromomethane, understanding the
hydrogen-1 nmr spectrum of bromomethane, explaining the line splitting patterns from
spin-spin coupling in the
high resolution H-1 nmr spectra of bromomethane, revising the H-1 nmr spectrum of
bromomethane,
proton nmr of bromomethane, ppm chemical shifts of the H-1 nmr spectrum of
bromomethane,
explaining and analyzing spin spin line splitting in the H-1 nmr spectrum, how
to construct the diagram of the H-1 nmr spectrum of bromomethane, how to work out the
number of chemically different protons in the structure of the bromomethane organic
molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR
spectrum of bromomethane using the n+1 rule to explain the spin - spin coupling ine
splitting in the proton nmr spectrum of bromomethane deducing the nature of the protons
from the chemical shifts ppm in the H-1 nmr spectrum of bromomethane
examining the 1H nmr spectrum of bromomethane analysing the 1-H nmr spectrum of
bromomethane how do you sketch and interpret the H-1 NMR spectrum of
bromomethane
interpreting interpretation of the 1H proton spin-spin coupling causing line
splitting in the NMR spectrum of bromomethane
assignment of chemical shifts in the
proton 1H NMR spectrum of bromomethane formula explaining spin-spin coupling for line splitting
methyl bromide
Links associated
with bromomethane
The chemistry of HALOGENOALKANES (haloalkanes)
revision notes INDEX
H-1 proton NMR spectroscopy index
(Please
read 8 points at the top of the 1H NMR index page)
ALL SPECTROSCOPY INDEXES
All Advanced Organic
Chemistry Notes
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