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Interpreting the H-1 hydrogen-1
(proton) NMR spectrum of
Pentane
[Author
©
Dr Phil Brown PhD:
Doc Brown's advanced level organic chemistry exam revision notes
suitable for students of UK A level chemistry courses & US K12 grade
11, grade 12 and AP honors chemistry courses:
Molecular
spectroscopy analysis of
pentane
[spectra page
updated Mar 26th 2026 *]
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1H NMR spectrum of
CH3(CH2)3CH3
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H-1 proton NMR spectroscopy -
spectra index
Links associated
with pentane
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and disclaimer]
See also
comparing the infrared, mass,
1H NMR and 13C NMR
spectra of the 3 alkane isomers of C5H12
Introductory note on the 1H NMR spectra of pentane
Students and teachers please note my explanation of the
proton NMR spectrum of pentane is designed for advanced, but
pre-university, chemistry courses.
The chemical shift
δ splitting pattern effects for
pentane are
confined to a proton spin-spin
coupling effects analysed using the n+1 rule for adjacent
non-equivalent proton fields (n is the number of neighbouring
protons in a non-equivalent different chemical environment for the
pentane molecule).
It is assumed that the integrated intensities of the
1H
NMR δ
chemical shifts give the ratio of the protons in the different
non-equivalent chemical environments of the pentane molecule.
The most common solvent used for investigating the 1H NMR
spectrum of compounds like pentane, is CDCl3 and other
deuterated solvents to avoid confusion with a 1H NMR
signal, 2D (2H) has a different NMR chemical
shift.
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 - pentane
here.
The chemical shifts quoted in ppm on the diagram of the
H-1 NMR spectrum of pentane represent the peaks of the intensity of the
chemical shifts of pentane (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
pentane molecule.
Pentane C5H12,
 ,
,
an alkane
For more
see The molecular structure and
naming of alkanes
Interpreting the H-1 NMR spectrum of
pentane
For relatively simple molecules, the low resolution H-1
NMR spectrum of pentane is a good starting point.
The hydrogen atoms
(protons) of pentane occupy 3 different chemical environments so that
the H-1 proton low resolution NMR spectra should show
three 1H chemical shift peaks (diagram above).
CH3CH2CH2CH2CH3
(note the ratio of the three colours of the
protons in pentane)
Although there are 12 hydrogen atoms in the molecule,
pentane is a symmetrical molecule with only
three possible chemical
environments for the 12 hydrogen atoms.
The peak area ratio of different chemical environments
is the same ratio as the number of protons that occupy these different situations.
The molecular proton ratios is 6 : 4 : 2, so the low resolution spectrum
should show 3 peaks in the
proton ratio of
3 : 2 : 1, from the integrated proton ratio from the
spectrum.
The high resolution spectrum of pentane is even more
complex than shown in the diagram.
CH3CH2CH2CH2CH3
has three different proton chemical environments
(a) From the n+1
rule the end CH3 group of protons (H3)
resonance lines are split into a
triplet by the neighbouring CH2 groups (H2),
at a chemical shift of
0.884 ppm).
CH3CH2CH2CH2CH3
(b) The two 'end' CH2 groups of protons (H2)
chemical shift is
split into a sextet (1:5:10:10:5:1) by CH2 (H2)
and CH3 (H3) groups
of protons (total of 5 protons),
centred around a chemical shift ~1.30 ppm.
CH3CH2CH2CH2CH3
(c) The chemical shift resonance of the central CH2 group
of protons (H2) is also split into a
quintet (1:4:6:4:1) by four protons from equivalent proton CH2 groups either side of it
(H2)
at a
chemical shift of 1.26 ppm).
The last two sets of chemical shift lines are
all bunched together - you need
very high resolution to sort out a septet of chemical shifts - all very
close together.
This sextet of resonances is characteristic of a
propyl group (CH3CH2CH2).
The splitting pattern from proton
spin-spin coupling effects is analysed using the n+1 rule for
adjacent non-equivalent proton fields (n is the number of
neighbouring protons in a non-equivalent different chemical
environment) and applied to the 1H NMR spectrum of
pentane.
|
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 |
|
3 |
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3 |
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1 |
|
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4
creates a quintet |
|
|
1 |
|
4 |
|
6 |
|
4 |
|
1 |
|
|
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5
creates a sextet |
|
1 |
|
5 |
|
10 |
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10 |
|
5 |
|
1 |
|
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6
creates a septet |
1 |
|
6 |
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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. |
 |
 |
 |
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 |
|
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. |
 |
 |
 |
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. |
 |
 |
 |
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. |
 |
 |
 |
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: Interpreting the proton H-1 NMR spectra of
pentane, low resolution & high resolution proton
nmr spectra of pentane, H-1 nmr spectrum of pentane, understanding the
hydrogen-1 nmr spectrum of pentane, explaining the line splitting patterns in the
high resolution H-1 nmr spectra of pentane, revising the H-1 nmr spectrum of
pentane,
proton nmr of pentane, ppm chemical shifts of the H-1 nmr spectrum of pentane,
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 pentane, how to work out the
number of chemically different protons in the structure of the pentane organic
molecule Molecular structure diagram of the
proton NMR diagram for the 1H NMR spectrum of pentane. The proton ratio in the
1H NMR spectrum of pentane. Deducing the number of different chemical
environments of the protons in the pentane molecule from the 1H chemical shifts
in the hydrogen-1 NMR spectrum of pentane. Analysing the high resolution 1H NMR
spectrum of pentane. Analysing the low resolution 1H NMR spectrum of pentane. You
may need to know the relative molecular mass of pentane to deduce the molecular
formula from the proton ratio of the 1H NMR spectrum of pentane. Revision notes
on the proton NMR spectrum of pentane. Matching and deducing the structure of
the pentane molecule from its hydrogen-1 NMR spectrum.
Proton NMR spectroscopy of alkane,
1H NMR spectra of pentane, an isomer of molecular formula
C5H12
How do you interpret the H-1 NMR spectrum of
pentane How to interpret
the H-1 NMR spectrum of pentane Explanatory diagram of the chemical
shifts of the 1H H-1 proton NMR spectrum of the pentane
molecule in terms of its molecular structure. Listing data of all the chemical shift peaks in ppm in the
proton NMR spectrum of pentane. How to explain the H-1 NMR spectrum of
pentane. The chemical shifts and integrated values of the proton ratios in the 1-H NMR
spectrum of the pentane molecule. How to work out the molecular
structure of the pentane molecule from its proton NMR spectrum. The uses
and distinctive features of the proton NMR spectrum of the pentane
molecule explained. What does the H-1 proton NMR spectrum chemical
shifts tell us about the
structure and properties of the pentane
molecule? explaining the spin-spin proton coupling effects in the 1H
NMR spectrum of pentane. interpretation
diagram explaining the proton splitting pattern produced from the
n+1 rule and the theoretical ratio of chemical shift
δ and values of
intensities for the proton NMR spectrum lines of pentane
Links associated
with pentane
The chemistry of ALKANES
revision notes INDEX
The infrared spectrum of pentane
The mass spectrum of Pentane
The C-13 NMR spectrum of Pentane
H-1 proton NMR spectroscopy index
(Please
read 8 points at the top of the 1H NMR index page)
ALL SPECTROSCOPY INDEXES
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Chemistry Notes
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