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The H-1
hydrogen-1 (proton) NMR spectrum of hexane
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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 hexane
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H-1 proton NMR spectroscopy -
spectra index
See also
comparing infrared, mass, 1H NMR & 13C NMR
spectra of the structural alkane isomers of C6H14
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 - hexane here.
The chemical shifts quoted in ppm on the diagram of
the H-1 NMR spectrum of hexane 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 hexane molecule.
Hexane C6H14,
,
,
For more
see The molecular structure,
classification and
naming of alkanes
Interpreting the
H-1 NMR spectrum of
hexane
For relatively simple molecules, the low
resolution H-1 NMR spectrum of hexane is a good starting point
(low resolution diagram above).
The hydrogen atoms (protons) of hexane occupy 3
different chemical environments so that the low resolution NMR
spectra should show 3 peaks of different H-1 NMR chemical shifts (diagram above for
hexane).
CH3CH2CH2CH2CH2CH3
Note the ratio
3:2:2 of the three colours of the protons
in the three chemically different environments
Although there are 14 hydrogen atoms in the molecule,
there only 3 possible chemical
environments for the hydrogen atoms in hexane molecule.
The integrated signal proton ratio
from the molecular structure
6:4:4 =
the 3:2:2 proton ratio observed, and corresponds with
the structural formula of hexane shown above.
The high resolution H-1 NMR
spectrum of hexane
In terms of spin-spin coupling from the possible proton magnetic orientations,
for hexane I
have only considered the interactions of
non-equivalent protons on adjacent carbon atoms
e.g. -CH2-CH3, -CH-CH2- protons
etc.
All low and high resolution spectra of hexane
show 3 groups of protons and in the ratio expected from the
formula of hexane.
The ppm quoted on the diagram represent the peak
of resonance intensity for a particular proton group in the
molecule of hexane - 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 hexane below.
So, using the chemical shifts and applying the
n+1 rule
to hexane
δ (a) 1H Chemical shift 0.89 ppm for
the 2 x CH3
protons CH3CH2CH2CH2CH2CH3
The CH3 proton resonance is
split into a 1:2:1 triplet by the adjacent CH2
protons, (n+1 = 3).
Evidence for the presence of a CH2 group
in the molecule of hexane
δ (b) 1H Chemical shift 1.29 ppm for
the 2 x 'outer' CH2
protons CH3CH2CH2CH2CH2CH3
This CH2 proton resonance is
split into a 1:5:10:10:5:1 sextet by the CH3
and CH2 protons on either side (n+1 = 6)
Evidence for the presence of a CH3CH2CH2 group
in the molecule of hexane
δ (c) 1H Chemical shift 1.27 ppm for
the 2 x 'central' CH2
protons CH3CH2CH2CH2CH2CH3
At first sight you would think this CH2 proton resonance is
split into a 1:4:6:4:1 quintet by the CH2 and
CH2 protons on either side (n+1 = 5).
However, theoretically, these particular
pairs of CH2 proton pairs are equivalent to each
other due to their central symmetry in the symmetrical
hexane molecule and should not split each other's
resonance.
Therefore, theoretically, this resonance
is just split by one the adjacent groups of CH2 protons
into a 1:2:1 triplet (n+1 = 3).
I would appreciate a second
opinion on this interpretation.
Very high resolution is needed to sort
out the
two CH2 resonances because the chemical
shifts are so close together.
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Comparing the infrared, mass, 1H NMR and 13C NMR
spectra of the five structural alkane isomers of C6H14
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 hexane,
2-methylpentane, 3-methylpentane, 2,2-dimethylbutane and
2,3-dimethylbutane image sizes. These five molecules
are structural isomers of saturated alkanes of molecular formula C6H14
and
exemplify the infrared, mass, 1H NMR and 13C NMR spectra of lower
aliphatic alkanes (non-cyclic alkanes). |
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Infrared spectra below. |
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INFRARED SPECTRA:
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. All the absorption
bands are typical of molecules containing saturated alkyl structure and
there are no characteristic infrared absorptions due to a specific
functional group. |
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Infrared spectra above, mass spectra below. |
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MASS SPECTRA: Base ion
peaks plus m/z comments.
Hexane: m/z 57, 42 and 56 prominent
2-methylpentane: m/z 43, 42 and 71 prominent
3-methylpentane: m/z 57, 41 and 56 prominent
2,2-dimethylbutane: m/z 43, 41, 57 and 71
prominent
2,3-dimethylbutane: m/z 43, 41, 42 and 71
prominent |
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Mass spectra above, 1H NMR spectra below. |
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1H NMR SPECTRA: They can
all be distinguished by their different integrated proton ratios -
need very high resolution.
Hexane:
3 1H
δ shifts, H ratio 3:2:2 (6:4:4 in formula)
2-methylpentane:
5 1H
δ shifts, H ratio 6:3:2:2:1
3-methylpentane:
4 1H
δ shifts, H ratio 6:4:3:1
2,2-dimethylbutane: 3 1H
δ shifts, H ratio 9:3:2
2,3-dimethylbutane: 2 1H
δ shifts, H ratio 6:1 (12:2 in formula) |
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1H NMR spectra above, 13C NMR spectra below. |
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13C NMR SPECTRA: From the
number of shifts, you can't distinguish (iii) and (iv) but you can
distinguish them from (i), (ii) and (v). (i) Hexane: 3 13C
δ shifts
(ii) 2-methylpentane: 5 13C
δ shifts
(iii) 3-methylpentane: 4 13C
δ shifts
(iv) 2,2-dimethylbutane: 4 13C
δ shifts
(v) 2,3-dimethylbutane: 2 13C
δ shifts |
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13C NMR spectra above. |
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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 |
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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 |
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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 |
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15 |
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6 |
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Key words & phrases: Interpreting the proton H-1 NMR spectra of hexane, low resolution & high resolution proton
nmr spectra of hexane, H-1 nmr spectrum of hexane, understanding the
hydrogen-1 nmr spectrum of hexane, explaining the line splitting patterns in the
high resolution H-1 nmr spectra of hexane, revising the H-1 nmr spectrum of
hexane,
proton nmr of hexane, ppm chemical shifts of the H-1 nmr spectrum of hexane,
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 hexane, how to work out the
number of chemically different protons in the structure of the hexane organic
molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR
spectrum of hexane using the n+1 rule to explain the spin - spin coupling ine
splitting in the proton nmr spectrum of hexane deducing the nature of the protons
from the chemical shifts ppm in the H-1 nmr spectrum of hexane
examining the 1H nmr spectrum of hexane analysing the 1-H nmr spectrum of
hexane how do you sketch and interpret the H-1 NMR spectrum of hexane
interpreting interpretation of the H-1 proton NMR spectrum of hexane
Molecular structure diagram of the
proton NMR diagram for the 1H NMR spectrum of hexane. The proton ratio in the
1H NMR spectrum of hexane. Deducing the number of different chemical
environments of the protons in the hexane molecule from the 1H chemical shifts
in the hydrogen-1 NMR spectrum of hexane. Analysing the high resolution 1H NMR
spectrum of hexane. Analysing the low resolution 1H NMR spectrum of hexane. You
may need to know the relative molecular mass of hexane to deduce the molecular
formula from the proton ratio of the 1H NMR spectrum of hexane. Revision notes
on the proton NMR spectrum of hexane. Matching and deducing the structure of
the hexane molecule from its hydrogen-1 NMR spectrum.
Proton NMR spectroscopy of aliphatic
alkanes,
1H NMR spectra of hexane, an isomer of molecular formula
C6H14
Links associated
with hexane
The chemistry of ALKANES
revision notes INDEX
The infrared spectrum of hexane
The mass spectrum of hexane
The H-1 NMR spectrum of hexane
The C-13 NMR spectrum of hexane
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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