|
Interpreting
and explaining
the H-1 (proton) NMR
spectrum of butan-2-ol
CH3CH(OH)CH2CH3
(2-butanol, sec-butanol, sec-butyl alcohol)
[Author
©
Dr
Phil Brown GRIC, PhD:
Doc Brown's advanced level pre-university/college organic chemistry exam revision notes
suitable for students of UK A level chemistry courses & US K12 grade 11,
grade 12 & AP honors chemistry courses: Molecular
spectroscopy
of
butan-2-ol
(2-butanol)
[spectrum page
updated
RE-EDIT]
email doc
brown
Re-edit
1H NMR spectrum of
CH3CH(OH)CH2CH3
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H-1 proton NMR spectroscopy -
spectra index
See also
Isomers of molecular formula
C4H10O
(Mr = 74)
Introductory note on the 1H NMR spectra of butan-2-ol
Students and teachers please note my explanation of the
proton NMR spectrum of butan-2-ol is designed for advanced, but
pre-university, chemistry courses.
The chemical shift
δ splitting pattern effects for
butan-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
butan-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 butan-2-ol molecule.
The most common solvent used for investigating the 1H NMR
spectrum of compounds like butan-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 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 - butan-2-ol here.
The chemical shifts quoted in ppm on the diagram of
the H-1 NMR spectrum of butan-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 butan-2-ol molecule.
Butan-2-ol C4H10O
A secondary alcohol
The molecular structure and naming of aliphatic
alcohols and ethers
Interpreting the
H-1 NMR spectrum of
butan-2-ol
In terms of spin-spin coupling from the possible proton magnetic orientations,
for butan-2-ol I
have only considered the interactions of
non-equivalent protons on adjacent carbon atoms
e.g. -CH2-CH3
protons.
For relatively simple molecules, the low
resolution H-1 NMR spectrum of butan-2-ol is a good starting point
(low resolution inset diagram above).
The hydrogen atoms (protons) of butan-2-ol occupy
5
different chemical environments so that the low resolution NMR
spectra should show 5 principal peaks of 5 different H-1 NMR chemical shifts (diagram above for
butan-2-ol).
CH3CH(OH)CH2CH3
Note the proton ratio 3:1:1:2:3 of the 5 colours of the protons
in the 5 chemically different environments
Chemical shifts
(a) to (e) on the H-1 NMR
spectrum diagram for butan-2-ol.
Although there are 10 hydrogen atoms in the molecule,
there are only 5 possible different chemical
environments for the hydrogen atoms in butan-2-ol molecule.
The integrated signal proton ratio 3:1:1:2:3 observed
in the high resolution H-1 NMR spectrum, corresponds with
the structural formula of butan-2-ol.
The high resolution 1H NMR
spectrum of butan-2-ol
All low and high resolution spectra of
butan-2-ol
show 5 groups of proton resonances and in the 3:1:1:2:3 ratio expected from the
formula of butan-2-ol.
The ppm quoted on the diagram represent the peak
of resonance intensity for a particular proton group in the
molecule of butan-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 butan-2-ol below.
So, using the chemical shifts and applying the
n+1 rule to
butan-2-ol
and make some predictions using some colour coding! (In problem
solving you work the other way round!)
BUT, an important note about the hydroxyl group on butan-2-ol (for
pre-university students):
Unless the alcohol is completely free of
water (difficult), the hydrogen on the -O-H
hydroxyl group and any hydrogens on the adjacent carbon
don't interact to produce any spin-spin splitting. Therefore
the -OH peak shows up as a singlet and you don't usually
have to consider its effect on any hydrogen atoms, if
present on the adjacent carbon atom (C-OH),
and, neither do you have to consider the splitting effect of
adjacent C-H protons on the hydrogen of the OH group.
(a) 1H
Chemical shift 1.17 ppm for methyl protons: CH3CH(OH)CH2CH3
This 1H resonance is split
into a 1:1 doublet by the adjacent CH proton (n+1 = 2).
Evidence for the presence of a CH group
in the molecule of butan-2-ol
(b) 1H
Chemical shift 3.71 ppm for CH proton: CH3CH(OH)CH2CH3
This 1H resonance is split
into a 1:5:10:10:5:1 sextet by the adjacent CH3
and CH2 protons on either side (n+1 = 6).
Evidence for the presence of a CH3-CHx-CH2 grouping
in the molecule of butan-2-ol
(c) 1H
Chemical shift 1.46 ppm for CH2 protons: CH3CH(OH)CH2CH3
This 1H resonance is split
into a 1:4:6:4:1 quintet by the adjacent CH3
and CH protons on either side (n+1 = 5).
Evidence for the presence of a CH-CHx-CH3 group
in the molecule of butan-2-ol
(d) 1H
Chemical shift 0.93 ppm for methyl protons: CH3CH(OH)CH2CH3
This 1H resonance is split
into a 1:2:1 triplet by the adjacent CH2
protons (n+2 = 3).
Evidence for the presence of a ? group
in the molecule of butan-2-ol
(e) 1H
Chemical shift 2.37 ppm for the hydroxyl proton: CH3CH(OH)CH2CH3
This 1H resonance is observed
as a singlet - assuming no splitting effect from the CH
proton.
Evidence for the presence of an O-H or
an 'isolated' C-H group
(no adjacent C-Hx) in the molecule of butan-2-ol,
but there is no isolated CH proton in the molecule.
Adding D2O to the sample under investigation,
dissolved in CDCl3, makes a significant
difference to the 1H NMR spectrum of butan-2-ol because
there
are
labile protons
to exchange with deuterium (2H) e.g. as in
alcohols (O-H)
or amines (N-H).
Therefore, because of proton exchange, the 1H
resonance is removed from the 1H NMR spectrum of
butan=2-ol.
Note the decreasing effect on the 1H chemical shift as the
proton is further from the more electronegative oxygen atom in butan-2-ol.
Butan-2-ol exhibits R/S optical
isomerism, but there would be no difference in their 1H NMR spectra as
far as I can ascertain.
Extra
note
on the OH proton resonance
If the alcohol is
impure, containing water or any source of labile protons, they 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
butan-2-ol, all
you usually see in the H-1 NMR spectrum is the mutual splitting of the
CH, CH2
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 butan-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 butan-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 butan-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 butan-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 butan-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 or greatly reduce the chemical shift for the OH proton from the 1H NMR
spectrum of butan-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
butan-2-ol molecule.
Key revision points about the 1H NMR spectrum of butan-2-ol (2-butanol)
A structured, exam‑ready breakdown of the ¹H NMR spectrum
of butan‑2‑ol (2‑butanol), tailored for advanced
pre‑university chemistry boards (AQA, Edexcel, OCR, WJEC, CCEA, CIE,
IB, AP Honors):
Key
Features of the ¹H NMR Spectrum of Butan‑2‑ol
- OH proton: Appears as a broad singlet, variable
chemical shift (~1–5 ppm depending on hydrogen bonding).
- CH adjacent to OH (secondary alcohol carbon):
Deshielded, ~3.4–4.0 ppm, multiplet due to coupling with
neighbouring
protons.
- CH3 groups:
- One methyl attached to the OH‑bearing carbon: ~1.0–1.2 ppm,
doublet (coupling with CH).
- Terminal methyl group: ~0.9 ppm, triplet (coupling with CH2).
- CH2 group: ~1.3–1.6 ppm, multiplet
(coupling with CH and CH3).
- Integration: Matches the number of protons in
each environment (total = 10 H).
Table of
Chemical Shifts, Origins, and Integration for the 1H NMR spectrum of
butan-2-ol (2-butanol)
| δ (ppm)
range |
Proton type |
Origin |
Splitting
pattern |
Integration |
| 0.9,
0.93 ppm |
CH3
(terminal) |
Methyl at end of chain |
Triplet (coupled to CH2) |
3H |
| 1.0–1.2,
1.17 |
CH3
(attached to OH‑bearing carbon) |
Methyl next to CH–OH |
Doublet (coupled to CH) |
3H |
| 1.3–1.6,
1.46 |
CH2 |
Methylene between CH and
terminal CH3 |
Multiplet |
2H |
| 3.4–4.0, 3.71 |
CH–OH |
Secondary carbon bearing OH |
Multiplet (coupled to CH3
and CH2) |
1H |
| 1–5,
2.37
(variable) |
OH |
Hydroxyl proton |
Broad singlet, exchangeable |
1H |
Spectra data source
https://sdbs.db.aist.go.jp/Disclaimer.aspx for
1H δ
ppm
Diagnostic
Effect of D2O
on the 1H NMR spectrum of butan-2-ol (2-butanol)
- When a drop of D2O
is added, the OH proton exchanges with deuterium (-O-H ==> -O-D).
- Result: The OH signal disappears (or is greatly
reduced) in the 1H NMR spectrum.
- Exam tip: This is a diagnostic test to confirm
the presence of an OH group.
Common
Student Misconceptions
- Thinking OH always appears at a fixed ppm: In
reality, it varies widely (1–5 ppm) depending on hydrogen bonding
and solvent.
- Misinterpreting OH splitting: OH protons often
appear as singlets due to rapid exchange; students sometimes expect
coupling.
- Confusing CH–OH with CH2 signals:
The deshielded CH near 3.5–4 ppm is distinctive.
- Forgetting integration ratios: Students may
miscount total protons; always check integration adds to 10.
- Not recognising D2O
effect: Some forget that OH disappears upon exchange, a
classic exam test.
Exam
Revision Tips
- Always match integration to molecular formula (C4H10O
= 10 H).
- Identify the deshielded CH near 3.5–4 ppm as the alcohol
carbon.
- Check for OH disappearance with D2O
— a diagnostic clue.
- Use splitting patterns to distinguish methyl groups:
- Terminal CH3
= triplet.
- CH3
next to CH–OH = doublet.
- Exam technique: When asked to assign signals,
state ppm, proton type, splitting, and integration (e.g., “Signal at
~0.9 ppm, triplet, 3H, terminal CH3”).
- Cross‑board consistency: All boards (AQA,
Edexcel, OCR, IB, AP) expect recognition of OH variability, D₂O
exchange, and correct assignment of proton environments.
Final
Guidance about the 1H NMR spectrum of butan-2-ol (2-butanol)
For A level and AP exams, focus on:
- Broad OH signal (variable, disappears with D2O).
- Deshielded CH at ~3.5–4 ppm.
- Two distinct methyl groups with different splitting
(triplet versus doublet).
- Integration adds to 10 protons.
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).
|
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 |
|
0
means no splitting |
|
|
|
|
|
|
1 |
|
|
|
|
|
|
|
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 |
Key words & phrases:
C4H10O
CH3CH(OH)CH2CH3 Interpreting the proton H-1 NMR spectra of butan-2-ol, low resolution & high resolution proton
nmr spectra of butan-2-ol, H-1 nmr spectrum of butan-2-ol, understanding the
hydrogen-1 nmr spectrum of butan-2-ol, explaining the line splitting patterns from
spin-spin coupling in the
high resolution H-1 nmr spectra of butan-2-ol, revising the H-1 nmr spectrum of
butan-2-ol,
proton nmr of butan-2-ol, ppm chemical shifts of the H-1 nmr spectrum of
butan-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 butan-2-ol, how to work out the
number of chemically different protons in the structure of the butan-2-ol organic
molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR
spectrum of butan-2-ol using the n+1 rule to explain the spin - spin coupling ine
splitting in the proton nmr spectrum of butan-2-ol deducing the nature of the protons
from the chemical shifts ppm in the H-1 nmr spectrum of butan-2-ol
examining the 1H nmr spectrum of butan-2-ol analysing the 1-H nmr spectrum of
butan-2-ol how do you sketch and interpret the H-1 NMR spectrum of butan-2-ol
interpreting interpretation of the 1H proton spin-spin coupling causing line
splitting in the NMR spectrum of butan-2-ol
assignment of chemical shifts in the
proton 1H NMR spectrum of butan-2-ol formula explaining spin-spin coupling for line splitting
in sec-butyl alcohol CH3CH2CH(OH)CH3 2-butanol How do you interpret the H-1 NMR spectrum of 2-butanol butan-2-ol How to interpret the H-1 NMR spectrum of 2-butanol butan-2-ol Explanatory diagram of the chemical shifts of the 1H H-1 proton NMR spectrum of the 2-butanol butan-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 2-butanol butan-2-ol. How to explain the H-1 NMR spectrum of 2-butanol butan-2-ol. The chemical shifts and integrated values of the proton ratios in the 1-H NMR spectrum of the 2-butanol butan-2-ol molecule. How to work out the molecular structure of the 2-butanol butan-2-ol molecule from its proton NMR spectrum. The uses and distinctive features of the proton NMR spectrum of the 2-butanol butan-2-ol molecule explained. What does the H-1 proton NMR spectrum chemical shifts tell us about the structure and properties of the 2-butanol butan-2-ol molecule?
How do you interpret the H-1 NMR spectrum of
butan-2-ol 2-butanol How to interpret
the H-1 NMR spectrum of butan-2-ol 2-butanol Explanatory diagram of the chemical
shifts of the 1H H-1 proton NMR spectrum of the butan-2-ol 2-butanol
molecule in terms of its molecular structure. Listing data of all the chemical shift peaks in ppm in the
proton NMR spectrum of butan-2-ol 2-butanol. How to explain the H-1 NMR spectrum of
butan-2-ol 2-butanol. The chemical shifts and integrated values of the proton ratios in the 1-H NMR
spectrum of the butan-2-ol 2-butanol molecule. How to work out the molecular
structure of the butan-2-ol 2-butanol molecule from its proton NMR spectrum. The uses
and distinctive features of the proton NMR spectrum of the
butan-2-ol 2-butanol
molecule explained. What does the H-1 proton NMR spectrum chemical
shifts tell us about the
structure and properties of the butan-2-ol 2-butanol
molecule? explaining the spin-spin proton coupling effects in the 1H
NMR spectrum of butan-2-ol 2-butanol.
interpretation
diagram explaining the proton splitting
pattern produced from the n+1 rule and the theoretical ratio of chemical shift
and values of intensities for the proton NMR spectrum lines of butan-2-ol
2-butanol
Links associated with butan-2-ol
See also
Isomers of molecular formula
C4H10O
(Mr = 74)
The infrared spectrum of butan-2-ol
(sec-butyl
alcohol)
The mass spectrum of butan-2-ol
(sec-butyl alcohol)
The C-13 NMR spectrum of
butan-2-ol (sec-butyl alcohol)
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 spectroscopy of butan-2-ol (2-butanol) - its 1H NMR spectrum,
diagnostic features, data analysed, useful infrared spectra exam revision
comments are
suitable for use of pre-university students studying AQA advanced level
chemistry, Edexcel advanced level chemistry, OCR advanced level chemistry, IB
advanced level chemistry, WJEC (Eduqas) advanced level chemistry, CIE Cambridge advanced level chemistry, US grade 11-12 AP honors
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