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Interpreting the
1H NMR spectrum of
3-methylbut-1-ene (3-methyl-1-butene)
[Author
©
Dr WP 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 - analysing the
1H NMR spectrum of
3-methylbut-1-ene
[updated
October 25th 2025]
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chemistry of ALKENES
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H-1 proton NMR spectroscopy -
spectra index
Introductory note on the 1H NMR spectra of 3-methylbut-1-ene
Students and teachers please note my explanation of the
proton NMR spectrum of 3-methylbut-1-ene is designed for advanced, but
pre-university, chemistry courses.
The chemical shift
δ splitting pattern effects for
3-methylbut-1-ene 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
3-methylbut-1-ene 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 3-methylbut-1-ene molecule.
The most common solvent used for investigating the 1H NMR
spectrum of compounds like 3-methylbut-1-ene, 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 - 3-methylbut-1-ene (3-methyl-1-butene) here.
In terms of spin-spin coupling from the possible proton magnetic orientations,
for 3-methylbut-1-ene I
have only considered the interactions of
non-equivalent protons on adjacent carbon atoms
e.g. -CH2-CH3
or >CH-CH3
or R-CH2-CH2-X
protons etc.
The chemical shifts quoted in ppm on the diagram of
the H-1 NMR spectrum of 3-methylbut-1-ene (3-methyl-1-butene) 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 3-methylbut-1-ene (3-methyl-1-butene) molecule.
3-methylbut-1-ene C5H10,
 ,
 ,
The molecular structure and naming of alkenes
Interpreting the
H-1 NMR spectrum of
3-methylbut-1-ene (3-methyl-1-butene)
For relatively simple molecules, the low
resolution H-1 NMR spectrum of 3-methylbut-1-ene
(3-methyl-1-butene) is a good starting point
(low resolution diagram above).
The hydrogen atoms (protons) of
3-methylbut-1-ene (3-methyl-1-butene) occupy 4
different chemical environments so that the low resolution NMR
spectra should show 4 peaks of different H-1 NMR chemical shifts (diagram above for
3-methylbut-1-ene (3-methyl-1-butene).
H2C=CHCH(CH3)2
Note the proton ratio 2:1:1:6 of the four colours of the protons
in the four chemically different environments
Chemical shifts
(a) to (d) on the H-1 NMR
spectrum diagram for 3-methylbut-2-ene.
Although there are 10 hydrogen atoms in the molecule,
there are only 4 possible different chemical
environments for the hydrogen atoms in 3-methylbut-1-ene
(3-methyl-1-butene) molecule.
The integrated signal proton ratio 2:1:1:6 is observed
on the high resolution H-1 NMR spectrum, corresponding with
the structural formula of 3-methylbut-1-ene (3-methyl-1-butene).
The high resolution H-1 NMR
spectrum of 3-methylbut-1-ene (3-methyl-1-butene)
All low and high resolution spectra of
3-methylbut-1-ene (3-methyl-1-butene)
show 4 groups of proton resonances and in the 2:1:1:6 ratio expected from the
formula of 3-methylbut-1-ene (3-methyl-1-butene).
The ppm quoted on the diagram represent the peak
of resonance intensity for a particular proton group in the
molecule of 3-methylbut-1-ene (3-methyl-1-butene) - 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 3-methylbut-1-ene (3-methyl-1-butene) below.
So, using the chemical shifts and applying the
n+1 rule to
3-methylbut-1-ene (3-methyl-1-butene)
and make some predictions using some colour coding! (In problem
solving you work the other way round!)
(a) 1H
Chemical shift 4.9 ppm
H2C
proton resonance
H2C=CHCH(CH3)2
The 'blue' proton resonance is split by
the 'purple' CH proton into 1:1 doublet (n+1 = 2).
The two
protons of the =CH2- group in
3-methylbut-1-ene are not absolutely equivalent to each
other because it is not a symmetrical alkene, so
technically, they occupy slightly different chemical
environments, but they are so similar that they give the
same H-1 NMR chemical shift of 4.9 ppm (at least to 1
d.p.).
Evidence for the presence of a CH group
in the molecule of 3-methylbut-1-ene (3-methyl-1-butene)
(b) 1H
Chemical shift 5.4 ppm CH
proton resonance
H2C=CHCH(CH3)2
The 'purple' CH proton resonance is
split by the 'blue' CH2 and 'green' CH
protons into a 1:3:3:1 quartet (n+1 = 4).
(c) 1H
Chemical shift 2.4 ppm CH
proton resonance
H2C=CHCH(CH3)2
The 'green' CH proton resonance is split
by the 'purple' CH proton and six 'brown' CH3
protons into a 1:7:21:35:35:21:7:1 octet (n+1 = 8).
(d) 1H
Chemical shift 1.0 ppm CH3
proton resonance
H2C=CHCH(CH3)2
The six 'brown' CH3 proton
resonance is split into a doublet by the 'green' CH
proton (n+1 = 2).
The six
protons of the two methyl groups in 3-methylbut-1-ene
are all equivalent to each other, the occupy the same
chemical environment and so give the same H-1 NMR
chemical shift of 1.0 ppm.
Evidence for the presence of a another
CH group
in the molecule of 3-methylbut-1-ene (3-methyl-1-butene)
Key points about the 1H
NMR spectrum of 3-methylbut-1-ene
Molecular Overview: 3-Methylbut-1-ene
Molecular formula:
C5H10
Structure:
This is a branched alkene with a terminal double bond and two methyl
groups.
Key Proton
Environments in ¹H NMR
|
Chemical Shift (δ, ppm) |
Proton
Type |
Environment |
Splitting Pattern |
Integration |
Notes |
|
~4.6–5.0, 4.9
ppm |
Vinyl protons (CH2=) |
Terminal alkene
(CH2=CH–) |
Doublet of
doublets |
2H |
Deshielded due to
C=C |
|
~5.7–6.2, 5.4
ppm |
Vinylic proton
(=CH–) |
Internal alkene
proton |
Multiplet |
1H |
Coupled to both
vinyl and alkyl protons |
|
~2.0–2.2, 2.4
ppm |
Allylic methine
(–CH–) |
CH bonded to CH3
and CH2=CH– |
Multiplet |
1H |
Slightly
deshielded by alkene |
|
~0.9–1.0, 1.0
ppm |
Methyl (CH–CH3)
x 2 |
2 Methyls on
branched carbon |
Doublet |
6H |
Split by adjacent
CH |
https://sdbs.db.aist.go.jp/
diagram δ ppm spectral database of organic
compounds
Proton
Assignments
- Vinyl region (δ ~4.6–6.2
ppm):
- Two protons on CH2=
(terminal alkene) and one on =CH– (internal alkene carbon).
- Allylic region (δ ~2.0
ppm):
- One proton on the methine
carbon adjacent to both the double bond and methyl groups.
- Alkyl region (δ ~0.9 ppm):
- Two methyl groups: one on the
terminal carbon, one on the branched carbon.
Common
Misconceptions
- Assuming all alkene
protons appear at the same shift
- Terminal vinyl protons (CH2=)
appear around 4.6–5.0 ppm, while internal alkene protons (=CH–)
are more downfield (~5.7–6.2 ppm).
- Overlooking coupling
patterns
- Vinyl protons often show
complex splitting due to coupling with adjacent protons (e.g.,
doublet of doublets).
- Confusing methyl signals
- Both methyl groups appear near
0.9 ppm but have different splitting: one is a doublet (CH3–CH),
the other a triplet (CH3–CH2).
- Ignoring integration
ratios
- Integration reflects the
number of protons: 2H (CH2=),
1H (=CH–), 1H (CH), 3H + 3H (CH3
groups).
Exam
Revision Tips
- Sketch the molecule:
Label each hydrogen environment to predict chemical shifts and
splitting.
- Use integration first:
Match peak areas to proton counts before assigning shifts.
- Look for alkene clues:
Vinyl protons are always downfield (>4.5 ppm) and often split.
- Check splitting logic:
Apply the n+1 rule based on adjacent protons.
- Compare isomers:
Practice with pent-1-ene, 2-methylbut-2-ene, etc., to distinguish
spectra.
- Don’t forget symmetry:
Equivalent protons give single signals (e.g., methyl groups if in
identical environments).
Tips for
Spotting Equivalent Methyl Groups in 1H NMR
e.g. the 2 methyl groups on C3 of 3-methylbut-1-ene
- Check for identical
attachments: If two
methyl groups are bonded to the same carbon and that carbon is not
chiral, they’re usually equivalent.
- Look for symmetry:
Even partial symmetry (like in 3-methylbut-1-ene) can lead to
equivalence.
- Use integration clues:
If two methyl groups give a single peak with integration of 6H,
that’s a strong hint they’re equivalent.
- Compare with isomers:
Try contrasting with 2-methylbut-2-ene or pent-2-ene, where methyl
environments differ more clearly.
- Counting methyls as
separate signals:
Leads to overestimating the number of peaks in ¹H NMR spectra.
- Assuming all methyls are
equivalent: Not true
in asymmetric or chiral environments.
- Ignoring branching effects:
Branching can create or remove equivalence depending on the
substitution pattern.
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
3-methylbut-1-ene.
|
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:
C5H10
Interpreting the proton H-1 NMR spectra of 3-methylbut-1-ene
(3-methyl-1-butene), low resolution & high resolution proton
nmr spectra of 3-methylbut-1-ene (3-methyl-1-butene), H-1 nmr spectrum of
3-methylbut-1-ene (3-methyl-1-butene), understanding the
hydrogen-1 nmr spectrum of 3-methylbut-1-ene (3-methyl-1-butene), explaining the line splitting patterns in the
high resolution H-1 nmr spectra of 3-methylbut-1-ene (3-methyl-1-butene), revising the H-1 nmr spectrum of
3-methylbut-1-ene (3-methyl-1-butene),
proton nmr of 3-methylbut-1-ene (3-methyl-1-butene), ppm chemical shifts of the H-1 nmr spectrum of
3-methylbut-1-ene (3-methyl-1-butene),
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 3-methylbut-1-ene
(3-methyl-1-butene), how to work out the
number of chemically different protons in the structure of the 3-methylbut-1-ene
(3-methyl-1-butene) organic
molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR
spectrum of 3-methylbut-1-ene (3-methyl-1-butene) using the n+1 rule to explain the spin - spin coupling
nmr
splitting in the proton nmr spectrum of 3-methylbut-1-ene (3-methyl-1-butene) deducing the nature of the protons
from the chemical shifts ppm in the H-1 nmr spectrum of 3-methylbut-1-ene
(3-methyl-1-butene)
examining the 1H nmr spectrum of 3-methylbut-1-ene (3-methyl-1-butene) analysing the 1-H nmr spectrum of
3-methylbut-1-ene (3-methyl-1-butene) how do you sketch and interpret the H-1
NMR spectrum of 3-methylbut-1-ene (3-methyl-1-butene)
interpreting interpretation of the H-1 proton NMR spectrum of 3-methylbut-1-ene
(3-methyl-1-butene)
C5H10
How do you interpret the H-1 NMR spectrum of 3-methylbut-1-ene
(3-methyl-1-butene) How to interpret
the H-1 NMR spectrum of 3-methylbut-1-ene (3-methyl-1-butene) Explanatory diagram of the chemical
shifts of the 1H H-1 proton NMR spectrum of the 3-methylbut-1-ene
(3-methyl-1-butene)
molecule in terms of its molecular structure. Listing data of all the chemical shift peaks in ppm in the
proton NMR spectrum of 3-methylbut-1-ene (3-methyl-1-butene). How to explain the H-1 NMR spectrum of
3-methylbut-1-ene (3-methyl-1-butene). The chemical shifts and integrated values of the proton ratios in the 1-H NMR
spectrum of the 3-methylbut-1-ene (3-methyl-1-butene) molecule. How to work out the molecular
structure of the 3-methylbut-1-ene (3-methyl-1-butene) molecule from its proton NMR spectrum. The uses
and distinctive features of the proton NMR spectrum of the
3-methylbut-1-ene (3-methyl-1-butene)
molecule explained. What does the H-1 proton NMR spectrum chemical
shifts tell us about the
structure and properties of the 3-methylbut-1-ene
(3-methyl-1-butene)
molecule? explaining the spin-spin proton coupling effects in the 1H
NMR spectrum of 3-methylbut-1-ene (3-methyl-1-butene).
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 3-methylbut-1-ene
(3-methyl-1-butene)
Links associated
with
3-methylbut-1-ene (3-methyl-1-butene)
The infrared spectrum of 3-methylbut-1-ene
The mass spectrum of 3-methylbut-1-ene
The C-13 NMR spectrum of
3-methylbut-1-ene
The chemistry of ALKENES
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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