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Interpreting the
1H NMR spectrum of propan-2-ol
CH3CH(OH)CH3
[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
propan-2-ol
[spectra page
updated Mar 26th 2026 *]
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doc brown re-edit 1H NMR spectrum of
CH3CHOHCH3
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H-1 proton NMR spectroscopy -
spectra index
Links associated with propan-2-ol
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See also
comparing the infrared, mass, 1H NMR and 13C NMR
spectra of the 3 isomers of C3H8O
Introductory note on the 1H NMR spectra of propan-2-ol
(2-propanol)
Students and teachers please note my explanation of the
proton NMR spectrum of propan-2-ol is designed for advanced, but
pre-university, chemistry courses.
The chemical shift
δ splitting pattern effects for
propan-2-ol 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
propan-2-ol 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 propan-2-ol molecule.
The most common solvent used for investigating the 1H NMR
spectrum of compounds like propan-2-ol, 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 - propan-2-ol here.
The chemical shifts quoted in ppm on the diagram of
the H-1 NMR spectrum of propan-2-ol 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 propan-2-ol molecule.
Propan-2-ol C3H8O,
,
,
 ,
secondary alcohol
The molecular structure and naming of aliphatic
alcohols and ethers
Interpreting the
H-1 NMR spectrum of
propan-2-ol (2-propanol, isopropyl alcohol)
For relatively simple molecules, the low
resolution H-1 NMR spectrum of propan-2-ol is a good starting point.
The hydrogen atoms (protons) of propan-2-ol occupy
3
different chemical environments so that the low resolution NMR
spectra should show
three 1H peaks of different H-1 NMR chemical shifts (diagram above for
propan-2-ol).
(CH3)2CHOH
or CH3CH(OH)CH3
Note the integrated
proton ratio of 6:1:1 of the 3 colours of the protons
in the 3 chemically different environments in the propan-2-ol
molecule.
Although there are 8 hydrogen atoms in the molecule,
there only 3 possible chemical
environments for the hydrogen atoms in propan-2-ol molecule.
The proton ratio of 6:1:1 observed in the 1H NMR
spectrum, corresponds with
the structural formula of propan-2-ol.
The high resolution spectrum
of propan-2-ol
All low and high resolution spectra of
propan-2-ol
show 3 groups of protons and in the ratio expected from the
formula of propan-2-ol.
The ppm quoted on the diagram represent the peak
of resonance intensity for a particular proton group in the
molecule of propan-2-ol - 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 propan-2-ol below.
So, using the chemical shifts and applying the
n+1 rule
to propan-2-ol
(a) Chemical shift 1.20 ppm the two CH3
groups of protons (6 equivalent protons)
The single CH proton splits the CH3
resonance into a 1:1 doublet (n+1 = 2).
Evidence for the presence of a CH group
in the molecule of propan-2-ol
(b) Chemical shift 4.01 ppm the lone CH
proton (1 proton)
The single CH proton is split by the 6
methyl protons into a 1:6:15:20:15:6:1 septet (n+1 = 7),
in terms of the relative intensities of the H-1 NMR
resonance lines.
Evidence for the presence a CH3-CHx-CH3 grouping
in the molecule of propan-2-ol (x = 2 or 1 as in the
case of propan-2-ol).
(c) Chemical shift 2.16 ppm the lone OH
proton (1 proton)
Generally speaking, unless ultra dry and
very high resolution, the hydroxyl proton resonance is
not split and neither does it cause a splitting effect
itself (see note at end).
Therefore you see a singlet resonance.
Note
on the OH proton resonance
If the alcohol is impure, containing water or
any source of labile protons, because water and the alcohol exchange protons
e.g.
R-O-H
+ H-O-H
R-O-H
+ H-O-H
This means the CH2 protons no
longer experience a 'simple' local field from one
singlet proton from two possible orientations, but, over
a finite period, experience the averaging effect of
exchanging protons.
This removes the spin - spin coupling effect and
the OH proton resonance just shows up as a singlet if the
butan-1-ol contains even a trace of water
(or acid).
This sort of exchange cannot happen with
the alkyl protons, but is common with molecules
containing a hydroxyl (OH) hydrogen atom like alcohols
and carboxylic acids.
Not only that, you also get proton transfer
between the alcohol molecules i.e.
R-O-H
+ H-O-R
R-O-H
+ H-O-R
which gives the same effect as traces of
water of acid.
So, in
propan-2-ol, all
you usually see in the H-1 NMR spectrum is the mutual splitting of the CH
and CH3 proton resonances plus a singlet line
for the OH proton resonance.
EXTRA NOTE on why the OH
proton chemical shift is usually observed as a singlet in alcohols
like propan-2-ol and how deuterium oxide can be used to identify the peak
caused by the hydroxyl proton
Although extremely weak acids, there
is constant exchanging of protons between alcohol
molecules
(R = alkyl groups of propan-2-ol).
R-O-H
+ H-O-R
R-O-H
+ H-O-R
The rate of proton transfer is increased by
traces of water.
R-O-H
+ H-O-H
R-O-H
+ H-O-H
This cannot happen with the non-acidic C-H
protons of alkyl groups in alcohols like propan-2-ol.
This rapid proton transfer interferes with the
field splitting effects of the hydroxyl O-H protons
and carbon C-H protons and the spin-spin
coupling effects disappear.
This phenomena can be used to identify the O-H
proton resonance from other C-H proton resonances in
hydroxyl molecules like propan-2-ol.
If deuterium oxide (D2O,
where D = 2H) is added to the NMR sample,
the 1H protons are rapidly replaced by
2H protons in the propan-2-ol molecule.
R-O-H
+ D-O-D
R-O-D
+ H-O-D
The 2H chemical shift frequency is
different to the 1H chemical shift
frequency, so the effect of D2O is to
remove the chemical shift for the OH proton from the 1H NMR
spectrum of propan-2-ol, thereby identifying the original
1H chemical shift as belonging to the
hydroxyl group O-H proton and not a C-H proton of the
propan-2-ol molecule.
|
Comparing the infrared, mass, 1H NMR and 13C NMR
spectra of the 3 isomers of C3H8O
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 propan-1-ol,
propan-2-ol and methoxyethane image sizes. |
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 |
 |
I wasn't able to obtain an infrared
spectrum for methoxyethane, so I've added the infrared spectrum
of ethoxyethane to enable a few comparisons with two aliphatic
alcohols
Comparing the
infrared
spectra of
propan-1-ol,
propan-2-ol and
methoxyethane
Propan-1-ol,
propan-2-ol and methoxyethane
are structural isomers of molecular formula C3H8O
Propan-1-ol,
propan-2-ol and methoxyethane
exemplify infrared spectra of the lower members of the homologous series
of aliphatic alcohols and ethers |
|
INFRARED SPECTRA
(above): There are, as expected, differences in the fingerprint region at
wavenumbers 1500 to 400 cm-1, but most absorptions
for all three molecules are the various C-O and the many C-H
vibrational modes. However, there is one characteristic distinguishing
absorption only present in the infrared spectra of alcohols, but
not in ethers, that is the broad O-H stretching vibration
peaking at ~3350 cm-1. There is also another broad
absorption band (origin?) peaking at ~650 cm-1 in the
alcohol spectra, but not in the ether spectra. |
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 |
 |
Comparing the
mass
spectra of
propan-1-ol,
propan-2-ol and
methoxyethane
Propan-1-ol,
propan-2-ol and methoxyethane
are structural isomers of molecular formula C3H8O
Propan-1-ol,
propan-2-ol and methoxyethane
exemplify the mass spectra of the lower members of the homologous series
of aliphatic alcohols and ethers |
|
MASS SPECTRA (above):
The base ion peaks are m/z 45 for propan-2-ol and methoxyethane,
but that of propan-1-ol is m/z 31. Many of the fragmentation
ions are common to all three spectra. The m/z 45 ion is peak is
much smaller in the propan-1-ol spectrum compared to the other
two. |
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|
 |
Comparing the
1H proton NMR
spectra of
propan-1-ol,
propan-2-ol and
methoxyethane
Propan-1-ol,
propan-2-ol and methoxyethane
are structural isomers of molecular formula C3H8O
Propan-1-ol,
propan-2-ol and methoxyethane exemplify the 1H proton NMR spectra of
the lower members of the homologous series of aliphatic alcohols and
ethers |
|
1H NMR SPECTRA (above): The 1H NMR spectra of
all three molecules give different integrated proton ratios for the
different 1H chemical environments i.e. the proton
ratios are as follows: propan-1-ol
3:2:2:1; propan-2-ol 6:1:1 and methoxyethane
3:2:3. Therefore, all three can be distinguished by their
1H NMR spectra. |
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 |
 |
Comparing the
carbon-13 NMR
spectra of
propan-1-ol,
propan-2-ol and
methoxyethane
Propan-1-ol,
propan-2-ol and methoxyethane
are structural isomers of molecular formula C3H8O
Propan-1-ol,
propan-2-ol and methoxyethane exemplify the carbon-13 NMR spectra of
members of the lower members of the homologous series of aliphatic
alcohols and ethers |
|
13C NMR SPECTRA
(above): The
13C NMR spectra of propan-1-ol and methoxyethane show
three different 13C NMR chemical shifts, but
propan-2-ol can be distinguished from the other two by
exhibiting only two chemical shift lines. You would need other
spectral data to distinguish propan-1-ol and methoxyethane. |
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
propan-2-ol.
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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 |
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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 |
|
4 |
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6 |
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4 |
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1 |
|
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5
creates a sextet |
|
1 |
|
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 |
|
6 |
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15 |
|
20 |
|
15 |
|
6 |
|
1 |
Key words & phrases: 2-propanol isopropyl
alcohol
Interpreting the proton H-1 NMR spectra of propan-2-ol, low resolution & high resolution proton
nmr spectra of propan-2-ol, H-1 nmr spectrum of propan-2-ol, understanding the
hydrogen-1 nmr spectrum of propan-2-ol, explaining the line splitting patterns in the
high resolution H-1 nmr spectra of propan-2-ol, revising the H-1 nmr spectrum of
propan-2-ol,
proton nmr of propan-2-ol, ppm chemical shifts of the H-1 nmr spectrum of
propan-2-ol,
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 propan-2-ol, how to work out the
number of chemically different protons in the structure of the propan-2-ol organic
molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR
spectrum of propan-2-ol using the n+1 rule to explain the spin - spin coupling ine
splitting in the proton nmr spectrum of propan-2-ol deducing the nature of the protons
from the chemical shifts ppm in the H-1 nmr spectrum of propan-2-ol
examining the 1H nmr spectrum of propan-2-ol analysing the 1-H nmr spectrum of
propan-2-ol how do you sketch and interpret the H-1 NMR spectrum of propan-2-ol
2-propanol isopropyl alcohol
isomer of molecular formula C3H8O
Molecular structure diagram of the
proton NMR diagram for the 1H NMR spectrum of propan-2-ol 2-propanol. The proton ratio in the
1H NMR spectrum of propan-2-ol 2-propanol. Deducing the number of different chemical
environments of the protons in the propan-2-ol 2-propanol molecule from the 1H chemical shifts
in the hydrogen-1 NMR spectrum of propan-2-ol 2-propanol. Analysing the high resolution 1H NMR
spectrum of propan-2-ol 2-propanol. Analysing the low resolution 1H NMR spectrum of
propan-2-ol 2-propanol. You
may need to know the relative molecular mass of propan-2-ol 2-propanol to deduce the molecular
formula from the proton ratio of the 1H NMR spectrum of propan-2-ol
2-propanol. Revision notes
on the proton NMR spectrum of propan-2-ol 2-propanol. Matching and deducing the structure of
the propan-2-ol 2-propanol molecule from its hydrogen-1 NMR spectrum.
Proton NMR spectroscopy of aliphatic alcohols,
1H NMR spectra of propan-2-ol 2-propanol, an isomer of molecular formula
C3H8O Explanatory diagram of the 1H H-1 proton NMR spectrum of the propan-2-ol 2-propanol molecule in terms of its molecular structure. Listing data of all the chemical shift peaks in ppm in the proton NMR spectrum of propan-2-ol 2-propanol. How to explain the H-1 NMR spectrum of propan-2-ol 2-propanol. The values of the integrated proton ratios in the 1-H NMR spectrum of the propan-2-ol 2-propanol molecule. How to work out the molecular structure of the propan-2-ol 2-propanol molecule from its proton NMR spectrum. The uses and distinctive features of the proton NMR spectrum of the propan-2-ol 2-propanol molecule explained. What does the H-1 proton NMR spectrum tell us about the structure and properties of the propan-2-ol 2-propanol molecule?
How do you interpret the H-1 NMR spectrum of
propan-2-ol How to interpret
the H-1 NMR spectrum of propan-2-ol Explanatory diagram of the chemical
shifts of the 1H H-1 proton NMR spectrum of the propan-2-ol
molecule in terms of its molecular structure. Listing data of all the chemical shift peaks in ppm in the
proton NMR spectrum of propan-2-ol. How to explain the H-1 NMR spectrum of
propan-2-ol. The chemical shifts and integrated values of the proton ratios in the 1-H NMR
spectrum of the propan-2-ol molecule. How to work out the molecular
structure of the propan-2-ol molecule from its proton NMR spectrum. The uses
and distinctive features of the proton NMR spectrum of the
propan-2-ol
molecule explained. What does the H-1 proton NMR spectrum chemical
shifts tell us about the
structure and properties of the propan-2-ol
molecule? explaining the spin-spin proton coupling effects in the 1H
NMR spectrum of propan-2-ol. 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 propan-2-ol
Links associated
with propan-2-ol
The chemistry of ALCOHOLS
revision notes INDEX
The infrared spectrum of Propan-2-ol (2-propanol,
isopropyl alcohol)
The mass spectrum of Propan-2-ol (2-propanol,
isopropyl alcohol)
The C-13 NMR spectrum
of Propan-2-ol (2-propanol,
isopropyl alcohol)
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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