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Interpreting the
hydrogen-1 NMR spectrum of methanol CH3OH
[Author
©
Dr Phil Brown GRIC, 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 methanol
[spectra page updated
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H-1 proton NMR spectroscopy -
spectra index
Practise exam questions on the 1H NMR spectrum of
methanol
with answers!
Introductory note on the 1H NMR spectra of methanol
Students and teachers please note my explanation of the
proton NMR spectrum of methanol is designed for advanced, but
pre-university, chemistry courses.
The chemical shift
δ splitting pattern effects for
methanol 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
methanol 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 methanol molecule.
The most common solvent used for investigating the 1H NMR
spectrum of compounds like methanol, 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 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 - methanol here.
In terms of spin-spin coupling from the possible proton magnetic orientations,
for methanol I
have only considered the interactions of
non-equivalent protons on adjacent carbon atoms
e.g. -CH2-OH.
The chemical shifts quoted in ppm on the diagram of
the H-1 NMR spectrum of methanol 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 methanol molecule.
Methanol CH4O
The molecular structure and naming of aliphatic
alcohols and ethers
Interpreting the
H-1 NMR spectrum of
methanol
For relatively simple molecules, the low
resolution H-1 NMR spectrum of methanol is a good starting point
(low resolution diagram above).
The hydrogen atoms (protons) of methanol occupy
2
different chemical environments so that the low resolution NMR
spectra should show 2 principal peaks of different H-1 NMR chemical shifts (diagram above for
methanol).
CH3OH
Note the
proton ratio 3:1 of the two colours of the protons
in the two chemically different environments
Chemical shifts
(a) and (b) on the H-1 NMR
spectrum diagram for methanol.
Although there are 4 hydrogen atoms in the molecule,
there are only 2 possible different chemical
environments for the hydrogen atoms in methanol molecule.
The integrated signal proton ratio 3:1 observed
in the high resolution H-1 NMR spectrum, corresponds with
the structural formula of methanol.
The high resolution 1H NMR
spectrum of methanol
All low and high resolution spectra of methanol
show 2 groups of proton resonances and in the 3:1 ratio expected from the
formula of methanol.
The ppm quoted on the diagram represent the peak
of resonance intensity for a particular proton group in the
molecule of methanol - 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 methanol below.
So, using the chemical shifts and applying the
n+1 rule to
methanol
and make some predictions using some colour coding! (In problem
solving you work the other way round!)
(a) 1H
Chemical shift 3.43 ppm, CH3 protons: CH3OH
This resonance is split into a 1:1
doublet by the adjacent OH proton (n+1 = 2)
Evidence for the presence of a methyl
group in the molecule of methanol'
However, most textbooks pre-university will say a singlet.
(b) 1H
Chemical shift 3.66 ppm. OH proton: CH3OH
Quite often
you don't see the splitting of the proton resonance for OH
group proton.
Therefore, you
might expect to see a singlet at the chemical shift δ of
3.66 ppm, and this is often observed by other alcohols e.g.
ethanol.
However, in
this case you can see evidence of hydroxy proton field split
by the three methyl group protons.
Theoretically,
the OH resonance is split into a 1:3:3:1
quartet by the adjacent CH3 protons (n+1 = 4),
which does theoretically provide evidence for a CH3 group
in the molecule of methanol.
From the diagram the
splitting seems to be more complex than this!
Note: At pre-university level the splitting
of the O-H proton resonance by the alkyl hydrogen atoms
isn't normally shown, but in this example I have.
So, most textbooks pre-university will say a singlet.
BUT, whatever
the complications,
the protons of methanol occupy two, and only two, different chemical environments.
In the
1H NMR spectrum of ethanol,
I've just shown the OH proton resonance as a singlet.
EXAM NOTE: UK A‑level exam boards do
not expect OH protons
to show spin–spin splitting, nor do they expect
students to predict or interpret any splitting
caused by OH protons. In exam conditions,
OH (alcohols, phenols) and NH (amines) signals are
always treated as singlets, because rapid
proton exchange removes observable coupling and what
you see is a broad singlet.
EXTRA NOTE on why the OH
proton chemical shift is usually observed as a singlet in alcohols
like methanol 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 methanol).
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 methanol.
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 methanol.
If deuterium oxide (D2O,
where D = 2H) is added to the NMR sample,
the 1H protons are rapidly replaced by
2H protons in the methanol 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 methanol, thereby identifying the original
1H chemical shift as belonging to the
hydroxyl group O-H proton and not a C-H proton of the
methanol molecule.
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QUESTIONS
Advanced A-level chemistry - practise exam questions on
the 1H NMR
spectrum of methanol
A
joint
AI-doc b re-edit experiment!
Jot
down your responses and check out the answers:
ANSWERS
If you think there are
any errors, please email me asap at
chem55555@hotmail.com
I don't mind if students/teachers do a selected printout
of these questions and answers.
Q1.
How many ¹H
NMR signals
does methanol show?
A. 3
B. 2 C. 1
D. 4
Q2.
The CH3
group
in methanol typically appears as:
A. A singlet
B. A doublet C. A triplet
D. A quartet
Q3.
The OH
proton
in methanol usually appears:
A. As a broad singlet
B. As a sharp triplet C. As a
quartet D. As a doublet
Q4.
Where does the
CH3
proton signal
typically appear (chemical shift)?
A. 0.5–1.0 ppm
B. 1.0–2.0 ppm C. 3.2–4.0 ppm
D. 6.0–8.0 ppm
Q5.
Where does the
OH proton
typically appear?
A. 0.5–1.0 ppm
B. 1.0–2.0 ppm C. 3.0–4.0 ppm
D. Variable, often 1–5 ppm
Q6.
What happens to methanol's
OH signal
when D2O
is added?
A. It becomes a triplet
B. It shifts downfield C. It
disappears D. It becomes sharper
Q7.
After adding D2O,
how many ¹H
NMR signals
remain?
A. 3
B. 2 C. 1
D. 0
Q8.
Which statement correctly describes the
splitting pattern
of methanol's CH3
group?
A. It is a singlet because
OH exchange is fast
B. It is a triplet because
OH has one proton
C. It is a quartet because
OH has one proton
D. It is a doublet because
OH couples strongly
Q9.
Which of the following would
not
change after adding D2O?
A. The OH signal
B. The number of signals
C. The CH3
chemical shift
D. The presence of OD in
the spectrum
Q10.
A student claims methanol's CH3
peak should split into a doublet because it is next
to OH. Why is this incorrect?
A. OH has no protons
B. OH protons do not split
CH3
due to rapid exchange
C. CH3
protons do not experience splitting
D. CH3
is too far from OH
Jot
down your responses and check out the answers:
ANSWERS
If you think there are
any errors, please email me asap at
chem55555@hotmail.com
I don't mind if students/teachers do a selected printout
of these questions and answers.
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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).
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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 |
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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 |
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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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1 |
Key words & phrases:
CH3OH
Interpreting the proton H-1 NMR spectra of
methanol, low resolution & high resolution proton
nmr spectra of methanol, H-1 nmr spectrum of methanol, understanding the
hydrogen-1 nmr spectrum of methanol, explaining the line splitting patterns in the
high resolution H-1 nmr spectra of methanol, revising the H-1 nmr spectrum of
methanol,
proton nmr of methanol, ppm chemical shifts of the H-1 nmr spectrum of methanol,
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 methanol, how to work out the
number of chemically different protons in the structure of the methanol organic
molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR
spectrum of methanol using the n+1 rule to explain the spin - spin coupling ine
splitting in the proton nmr spectrum of methanol deducing the nature of the protons
from the chemical shifts ppm in the H-1 nmr spectrum of methanol
examining the 1H nmr spectrum of methanol analysing the 1-H nmr spectrum of
methanol how do you sketch and interpret the H-1 NMR spectrum of methanol
interpreting interpretation of the 1H proton NMR spectrum of methanol
methyl alcohol
explaining spin-spin coupling causing line splitting Explanatory diagram of the 1H H-1 proton NMR spectrum of the methanol molecule in terms of its molecular structure. Listing data of all the chemical shift peaks in ppm in the proton NMR spectrum of methanol. How to explain the H-1 NMR spectrum of methanol. The values of the integrated proton ratios in the 1-H NMR spectrum of the methanol molecule. How to work out the molecular structure of the methanol molecule from its proton NMR spectrum. The uses and distinctive features of the proton NMR spectrum of the methanol molecule explained. What does the H-1 proton NMR spectrum tell us about the structure and properties of the methanol molecule?
How do you interpret the H-1 NMR spectrum of
methanol How to interpret
the H-1 NMR spectrum of methanol Explanatory diagram of the chemical
shifts of the 1H H-1 proton NMR spectrum of the methanol
molecule in terms of its molecular structure. Listing data of all the chemical shift peaks in ppm in the
proton NMR spectrum of methanol. How to explain the H-1 NMR spectrum of
methanol. The chemical shifts and integrated values of the proton ratios in the 1-H NMR
spectrum of the methanol molecule. How to work out the molecular
structure of the methanol molecule from its proton NMR spectrum. The uses
and distinctive features of the proton NMR spectrum of the methanol
molecule explained. What does the H-1 proton NMR spectrum chemical
shifts tell us about the
structure and properties of the methanol
molecule? explaining the spin-spin proton coupling effects in the 1H
NMR spectrum of methanol. 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 methanol
Links associated
with methanol
The mass spectrum of methanol
The C-13 NMR spectrum of
methanol
The infrared spectrum of methanol
The chemistry of ALCOHOLS
revision notes INDEX
H-1 proton NMR spectroscopy index
(Please
read 8 points at the top of the 1H NMR index page)
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The
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chemistry of carboxylic acids and derivatives The chemistry of
organo-nitrogen compounds
The chemistry of
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are unofficial. These organic chemistry revision notes on
spectroscopy (1H NMR spectrum of methanol, explanations of
the detailed analysis and how to interpret the spectra notes)
are
suitable for use of pre-university students studying AQA advanced level
chemistry, Edexcel advanced level chemistry, OCR advanced level
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chemistry courses and they will also prove useful to
1st year undergraduate students of chemistry.
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ANSWERS
Advanced A-level chemistry - practise exam questions on
the 1H NMR
spectrum of methanol
If you think there are
any errors, please email me asap at
chem55555@hotmail.com
I don't mind if students/teachers do a selected printout
of these questions and answers.
Q1.
How many ¹H
NMR signals
does methanol show?
A. 3
B. 2 C. 1
D. 4
Correct answer: B
Explanation:
Methanol has
two types of protons:
So it shows
two signals.
Common
misconception:
Students sometimes think the OH proton “doesn't
count” because it exchanges — but it
still appears
unless D2O is added.
Q2.
The CH3
group
in methanol typically appears as:
A. A singlet
B. A doublet C. A triplet
D. A quartet
Correct answer: A
Explanation:
The CH3
protons do
not reliably couple
with the OH proton because OH exchange is fast.
Therefore, in this case, the CH3
signal is usually a
singlet.
Common
misconception:
Students often expect a doublet (3 H next to 1 H),
but OH coupling is
not observed
under normal conditions - but I did mention it.
Q3.
The OH
proton
in methanol usually appears:
A. As a broad singlet
B. As a sharp triplet C. As a
quartet D. As a doublet
Correct answer: A
Explanation:
The OH proton exchanges rapidly, giving a
broad singlet.
Common
misconception:
Students sometimes think OH must split the CH3
group — but rapid exchange prevents this.
Q4.
Where does the
CH3
proton signal
typically appear (chemical shift)?
A. 0.5–1.0 ppm
B. 1.0–2.0 ppm C. 3.2–4.0 ppm
D. 6.0–8.0 ppm
Correct answer: C
Explanation:
The CH3
group is attached to oxygen, which
deshields
the protons, shifting them downfield to
~3.3 ppm.
Common
misconception:
Students often place CH₃ groups at ~1 ppm,
forgetting that electronegative atoms shift signals
downfield.
Q5.
Where does the
OH proton
typically appear?
A. 0.5–1.0 ppm
B. 1.0–2.0 ppm C. 3.0–4.0 ppm
D. Variable, often 1–5 ppm
Correct answer: D
Explanation:
OH protons are
highly variable,
depending on hydrogen bonding and solvent.
Common
misconception:
Students sometimes think OH always appears at ~1 ppm
— but its position is
not reliable.
Q6.
What happens to methanol's
OH signal
when D2O
is added?
A. It becomes a triplet
B. It shifts downfield C. It
disappears D. It becomes sharper
Correct answer: C
Explanation:
The OH proton exchanges with deuterium: CH3OH
+ D2O → CH3OD
+ HOD Deuterium does
not
appear in ¹H NMR, so the OH signal
vanishes.
Common
misconception:
Students sometimes think the OH peak “moves” — it
actually
disappears
because 1H NMR spectrometers do not pick up the -D
signal.
Q7.
After adding D2O,
how many ¹H
NMR signals
remain?
A. 3
B. 2 C. 1
D. 0
Correct
answer: C
Explanation:
Only the
CH3 protons
remain, giving
one signal.
Common
misconception:
Students sometimes think CH3 splits because OD
is present — but OD does
not
couple in ¹H NMR.
Q8.
Which statement correctly describes the
splitting pattern
of methanol's CH3
group?
A. It is a singlet because
OH exchange is fast
B. It is a triplet because
OH has one proton
C. It is a quartet because
OH has one proton
D. It is a doublet because
OH couples strongly
Correct
answer: A
Explanation:
Rapid OH exchange prevents coupling, so CH3
appears as a
singlet.
Common
misconception:
Students apply the n+1 rule mechanically without
considering
exchange effects.
Q9.
Which of the following would
not
change after adding D2O?
A. The OH signal
B. The number of signals
C. The CH3
chemical shift
D. The presence of OD in
the spectrum
Correct
answer: C
Explanation:
The CH3
group remains unchanged; only the OH
proton is replaced.
Common
misconception:
Students sometimes think CH3
shifts because “the
molecule changed,” but OD does not affect the
CH3
environment significantly.
Q10.
A student claims methanol's CH3
peak should split into a doublet because it is next
to OH. Why is this incorrect?
A. OH has no protons
B. OH protons do not split
CH3
due to rapid exchange
C. CH3
protons do not experience splitting
D. CH3
is too far from OH
Correct
answer: B, but for low resolution.
Explanation:
OH protons exchange rapidly with solvent, so
they do
not couple
with CH3.
Common
misconception:
Students often apply the n+1 rule without
considering
dynamic processes
like proton exchange.
If you think there are
any errors, please email me asap at
chem55555@hotmail.com
I don't mind if students/teachers do a selected printout
of these questions and answers.
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