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The H-1
hydrogen-1 (proton) NMR spectrum of 2-methylbutane
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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 2-methylbutane
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H-1 proton NMR spectroscopy -
spectra index
See also
comparing the infrared, mass,
1H NMR and 13C NMR
spectra of the 3 alkane isomers of C5H12
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 shifts, called chemical shifts, depend on the
individual (electronic) chemical environment of the hydrogen atoms
in an organic molecule - 2-methylbutane here.
The chemical shifts quoted in ppm on the diagram of
the H-1 NMR spectrum of 2-methylbutane 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-methylbutane molecule.
2-methylbutane C5H12
 ,
,
For more
see The molecular structure and
naming of alkanes
Interpreting the
H-1 NMR spectrum of
2-methylbutane
For relatively simple molecules, the low
resolution H-1 NMR spectrum of 2-methylbutane is a good starting point.
The hydrogen atoms (protons) of 2-methylbutane occupy
4
different chemical environments so that the low resolution NMR
spectra should show 4 peaks of different H-1 NMR chemical shifts (low
resolution diagram above for
2-methylbutane).
(CH3)2CHCH2CH3
Note the integrated proton ratio 6:1:2:3 of the 4 colours of the protons
in the 4 chemically different environments
Although there are 12 hydrogen atoms in the molecule,
there only 4 possible 1H chemical
environments for the hydrogen atoms in 2-methylbutane molecule.
The proton ratio 6:1:2:3 observed, corresponds with
the structural formula of 2-methylbutane.
The high resolution spectrum
of 2-methylbutane
All low and high resolution spectra of
2-methylbutane
show 4 groups of protons and in the ratio expected from the
structural formula of 2-methylbutane.
The ppm quoted on the diagram represent the peak
of resonance intensity for a particular proton group in the
molecule of 2-methylbutane - since the peak' is at the apex of a band of
H-1 NMR resonances due to spin - spin coupling field splitting effects - see high resolution
notes on 2-methylbutane below.
So, using the chemical shifts and applying the
n+1 rule
to 2-methylbutane
(a) Chemical shift 0.869 ppm, the left-hand
2
x CH3
protons,
(CH3)2CHCH2CH3
This proton resonance is split into a
1:1 doublet by the CH proton (n+1 = 2 = doublet).
Evidence for the presence of a CH group
in the molecule of 2-methylbutane
(b) Chemical shift 1.45 ppm, the lone CH
proton,
(CH3)2CHCH2CH3
This proton resonance is split into a
nonet (n+1 = 9 because of 2 x CH3 plus CH2)
Evidence for the presence of a (CH3)2CHCH2
group in the molecule of 2-methylbutane.
(c) Chemical shift 1.20 ppm, the CH2
protons,
(CH3)2CHCH2CH3
This proton resonance is split into a
1:4:6:4:1 quintet by the CH proton and the right-hand CH3
group protons (n+1 = 5).
(d) Chemical shift 0.865 ppm, the right-hand
CH3
protons,
(CH3)2CHCH2CH3
This proton resonance is split into a
1:2:1 triplet by the CH2 protons (n+1 = 3)
Evidence for the presence of a CH2 group
in the molecule of 2-methylbutane
|
Number of protons 1H
causing splitting |
Splitting pattern produced from the
n+1 rule and the theoretical ratio of line intensities |
| 0
means no splitting |
|
|
|
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|
1 |
|
|
|
|
|
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| 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 |
|
Comparing the infrared, mass, 1H NMR and 13C NMR
spectra of the 3 alkane isomers of C5H12
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 pentane,
2-methylbutane and 2,2-dimethylpropane image sizes. |
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Comparing the
infrared
spectra of pentane, 2-methylbutane and 2,2-dimethylpropane
Pentane,
2-methylbutane and 2,2-dimethylpropane
are structural isomers of molecular formula C5H12
Pentane,
2-methylbutane and 2,2-dimethylpropane
exemplify infrared spectra of the alkane homologous series CnH2n+2
hydrocarbon
molecules, where n = 5 |
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INFRARED SPECTRA
(above): There are, as expected, differences in the fingerprint region at
wavenumbers 1500 to 400 cm-1, but there is no
specific infrared absorption band for a functional group. The
infrared spectra of pentane and 2-methylbutane seem very
similar, but that of 2,2-dimethylpropane seems much simpler. |
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 |
 |
Comparing the
mass
spectra of pentane, 2-methylbutane and 2,2-dimethylpropane
Pentane,
2-methylbutane and 2,2-dimethylpropane
are structural isomers of molecular formula C5H12
Pentane,
2-methylbutane and 2,2-dimethylpropane
exemplify the mass spectra of the alkane series CnH2n+2
hydrocarbon
molecules, where n = 5 |
|
MASS SPECTRA (above):
All three hydrocarbons show some similarities in their mass
spectra e.g. m/z ions 27 to 29 for [C2Hx]+
(x = 2 and 4). The molecular ion peaks will
be the same for all three isomers (m/z 72),
but it is very tiny for 2,2-dimethypropane. The pattern ratios
for m/z 39 to 43 are similar for pentane and 2-methylbutane, but
m/z 42 and 43 ions are almost absent from the
2,2-dimethylpropane spectrum. The base peak ion for pentane is
m/z 43, but for 2-methylbutane and 2,2-dimethylpropane it is m/z
57. |
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 |
 |
Comparing the
1H proton NMR
spectra of pentane, 2-methylbutane and 2,2-dimethylpropane
Pentane,
2-methylbutane and 2,2-dimethylpropane
are structural isomers of molecular formula C5H12
Pentane,
2-methylbutane and 2,2-dimethylpropane exemplify the 1H proton NMR spectra of the alkane
homologous series CnH2n+2
hydrocarbon
molecules where, n = 5 |
|
1H NMR SPECTRA (above): The 1H NMR spectra of
all three molecules give different proton ratios for the
different 1H chemical environments i.e. pentane's
proton ratio is 3:2:1 (from 6:4:2 H's in the molecule).
2-methylbutane's proton ratio is 6:1:2:3 and
2,2-dimethylpropane's doesn't have a proton ratio, all hydrogen
atoms are equivalent. This means all three isomeric C5H12
hydrocarbons can be distinguished from their 1H NMR spectra. |
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 |
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Comparing the
carbon-13 NMR
spectra of pentane, 2-methylbutane and 2,2-dimethylpropane
Pentane,
2-methylbutane and 2,2-dimethylpropane
are structural isomers of molecular formula C5H12
Pentane,
2-methylbutane and 2,2-dimethylpropane exemplify the carbon-13 NMR spectra of
members of the alkane homologous series CnH2n+2
hydrocarbon
molecules, where n = 5 |
|
13C NMR SPECTRA
(above): The
13C NMR spectra of the three molecules show different numbers of
carbon-13 chemical environments i.e different numbers of 13C NMR
resonance lines. So, pentane gives three 13C chemical
shifts,
2-methylbutane four and 2,2-dimethylpropane two. This means all
three isomeric C5H12 hydrocarbons can be
distinguished from their 13C NMR spectra. |
Key words & phrases:
isopentane methylbutane Interpreting the proton H-1 NMR spectra of
2-methylbutane, low resolution & high resolution proton
nmr spectra of 2-methylbutane, H-1 nmr spectrum of 2-methylbutane, understanding the
hydrogen-1 nmr spectrum of 2-methylbutane, explaining the line splitting patterns in the
high resolution H-1 nmr spectra of 2-methylbutane, revising the H-1 nmr spectrum of
2-methylbutane,
proton nmr of 2-methylbutane, ppm chemical shifts of the H-1 nmr spectrum of
2-methylbutane,
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 2-methylbutane, how to work out the
number of chemically different protons in the structure of the 2-methylbutane organic
molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR
spectrum of 2-methylbutane using the n+1 rule to explain the spin - spin coupling ine
splitting in the proton nmr spectrum of 2-methylbutane deducing the nature of the protons
from the chemical shifts ppm in the H-1 nmr spectrum of 2-methylbutane
examining the 1H nmr spectrum of 2-methylbutane analysing the 1-H nmr spectrum of
2-methylbutane how do you sketch and interpret the H-1 NMR spectrum of
2-methylbutane isopentane methylbutane
Molecular structure diagram of the
proton NMR diagram for the 1H NMR spectrum of 2-methylbutane. The proton ratio in the
1H NMR spectrum of 2-methylbutane. Deducing the number of different chemical
environments of the protons in the 2-methylbutane molecule from the 1H chemical shifts
in the hydrogen-1 NMR spectrum of 2-methylbutane. Analysing the high resolution 1H NMR
spectrum of 2-methylbutane. Analysing the low resolution 1H NMR spectrum of
2-methylbutane. You
may need to know the relative molecular mass of 2-methylbutane to deduce the molecular
formula from the proton ratio of the 1H NMR spectrum of 2-methylbutane. Revision notes
on the proton NMR spectrum of 2-methylbutane. Matching and deducing the structure of
the 2-methylbutane molecule from its hydrogen-1 NMR spectrum.
Proton NMR spectroscopy of aliphatic alkanes,
1H NMR spectra of 2-methylbutane, an isomer of molecular formula
C5H12
Links associated
with 2-methylbutane
The chemistry of ALKANES
revision notes INDEX
The infrared spectrum for
2-methylbutane
The mass spectrum for 2-methylbutane
The C-13 NMR spectrum for
2-methylbutane
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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