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Interpreting the
1H NMR spectrum of 2-methylpentane
[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 - analysing the
1H NMR spectrum of
2-methylpentane
[spectra
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CH3CH2CH2CH(CH3)2
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H-1 proton NMR spectroscopy -
spectra index
See also
comparing infrared, mass, 1H NMR & 13C NMR
spectra of the structural alkane isomers of C6H14
Introductory note on the 1H NMR spectra of 2-methylpentane
Students and teachers please note my explanation of the
proton NMR spectrum of 2-methylpentane is designed for advanced, but
pre-university, chemistry courses.
The chemical shift
δ splitting pattern effects for
2-methylpentane 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
2-methylpentane 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 2-methylpentane molecule.
The most common solvent used for investigating the 1H NMR
spectrum of compounds like 2-methylpentane, 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 - 2-methylpentane here.
The chemical shifts quoted in ppm on the diagram of
the H-1 NMR spectrum of 2-methylpentane 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 2-methylpentane molecule.
2-methylpentane C6H14,
 ,
,
For more
see The molecular structure,
classification and
naming of alkanes
Interpreting the
H-1 NMR spectrum of
2-methylpentane
In terms of spin-spin coupling from the possible proton magnetic orientations,
I
have only considered the interactions of
non-equivalent protons on adjacent carbon atoms
e.g. -CH2-CH3, -CH2-CH- protons
etc.
For relatively simple molecules, the low
resolution H-1 NMR spectrum of 2-methylpentane is a good starting point
(low resolution inset diagram above).
The hydrogen atoms (protons) of 2-methylpentane occupy
5
different chemical environments so that the low resolution NMR
spectra should show 5 peaks of different H-1 NMR chemical shifts (diagram above for
2-methylpentane).
(CH3)2CHCH2CH2CH3
Note the ratio
6:1:2:2:3 of the five colours of the protons
in the five chemically different environments
Although there are 14 hydrogen atoms in the molecule,
theoretically there only 5 possible chemical
environments for the hydrogen atoms in 2-methylpentane molecule.
The integrated signal proton ratio 6:1:2:2:3 observed, corresponds with
the structural formula of 2-methylpentane.
The high resolution H-1 NMR
spectrum of 2-methylpentane
All low and high resolution spectra of
2-methylpentane
should show 5 groups of protons and in the ratio expected from the
formula of 2-methylpentane, but some 1H NMR chemical shifts are
very close together.
The ppm quoted on the diagram represent the peak
of resonance intensity for a particular proton group in the
molecule of 2-methylpentane - 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 2-methylpentane below.
So, using the chemical shifts and applying the
n+1 rule
to 2-methylpentane.
I've dealt with them from left to right on a colour coded basis
for proton resonance lines (a) to (e).
δ
(a)
1H
Chemical shift of the 'blue' CH3 protons
(CH3)2CHCH2CH2CH3
A doublet at 0.86 ppm, the six (CH3)2
group protons resonance is split into a doublet
resonance by the adjacent CH proton (n+1 = 2).
The six
protons of the left-hand methyl groups are equivalent to
each other in 2-methylpentane, so they give identical
chemical shifts because of being in identical chemical
environments.
Evidence for the presence of a CH group
in the molecule of 2-methylpentane.
δ
(b)
1H
Chemical shift of CH proton
(CH3)2CHCH2CH2CH3
A nonet at 1.54 ppm, the CH proton
resonance is split by the 6 adjacent CH3
protons and 2 CH2 protons (n+1 = 9).
Evidence for the presence of a (CH3)2CHCH2 group
in the molecule of 2-methylpentane
δ
(c)
1H
Chemical shift of the 'green' CH2 protons
(CH3)2CHCH2CH2CH3
A quartet at 1.15 at ppm, the CH2
protons resonance is split by the adjacent CH proton and
CH2 protons (n+1 = 4)
Evidence for the presence of a CHCH2CH2 group
in the molecule of 2-methylpentane
δ
(d)
1H
Chemical shift of 'brown' CH2 protons
(CH3)2CHCH2CH2CH3
A sextet at 1.29 ppm, the CH2
protons resonance is split by the adjacent CH2
protons and CH3 protons (n+1 = 6)
Evidence for the presence of a CH2CH2CH3 group
in the molecule of 2-methylpentane
δ
(e)
1H
Chemical shift of CH3 protons
(CH3)2CHCH2CH2CH3
A triplet at 0.88 ppm, for the
'right-hand' CH3
protons resonance, which is split by the adjacent CH2 protons (n+1 = 3)
Evidence for the presence of a another
CH3 group
in the molecule of 2-methylpentane
Summary of the 1H NMR spectrum of
2-methylpentane
The ¹H NMR spectrum of 2-methylpentane shows five distinct proton
environments with chemical shifts between 0.9–1.4 ppm, all in the
alkyl region.
The spectrum is dominated by methyl and methylene signals, with the
most downfield shift near the branched carbon.
Key Proton Environments in
2-Methylpentane
2-Methylpentane (C6H14)
is a branched alkane with no electronegative atoms or π systems, so
all proton signals appear in the upfield region. Here's a breakdown
of the chemical shifts and integration:
| Chemical Shift (δ,
ppm) |
Proton Type |
Environment |
Integration |
| ~0.90,
0.86 ppm |
CH3 |
Terminal methyls (–CH3
at C2) |
6H (2×CH3) |
| ~0.95,
0.88 ppm |
CH3 |
End methyl (–CH3
at C5) |
3H |
| ~1.20,
1.15 and 1.29 ppm |
CH2 |
Methylene (–CH2–
at C3 and C4) |
4H (2×CH2) |
| ~1.40,
1.54 ppm |
CH |
Methine (–CH– at C2) |
1H |
Sources: ChemicalBook spectrum data,
Heriot-Watt NMR handout
Common Misconceptions in ¹H NMR
Interpretation
- Assuming all methyl groups
are equivalent: In
branched alkanes, methyl groups near branching (like the one at C2)
are chemically distinct and appear at slightly different shifts.
- Expecting downfield shifts:
Without electronegative atoms or π systems, all signals appear
upfield (δ < 2 ppm).
- Overlooking symmetry:
Students may miss that two terminal methyl groups are equivalent,
simplifying the spectrum.
Exam Revision Tips for ¹H NMR
Spectroscopy
These tips apply across AQA, Edexcel,
OCR, WJEC, CCEA, CIE, IB, and US AP Chemistry syllabi:
- Master the alkyl region:
For alkanes, expect δ = 0.8–1.5 ppm. Learn to distinguish CH3,
CH2,
and CH signals.
- Use integration wisely:
Match proton counts to molecular formula. For C6H14,
expect 14 protons total.
- Multiplicity matters:
Use splitting patterns (n+1 rule) to identify adjacent protons:
- CH3
next to CH2
→ triplet
- CH2
next to CH3
→ quartet
- CH next to CH3
and CH2
→ multiplet
- Draw the structure:
Label each hydrogen environment to predict shifts and splitting.
- Compare spectra:
Practice with straight-chain versus branched alkanes to see how
branching affects chemical shifts and multiplicity.
- Combine with IR and MS:
Exams often require deducing structure from multiple spectra.
|
Comparing the infrared, mass, 1H NMR and 13C NMR
spectra of the five structural alkane isomers of C6H14
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 hexane,
2-methylpentane, 3-methylpentane, 2,2-dimethylbutane and
2,3-dimethylbutane image sizes. These five molecules
are structural isomers of saturated alkanes of molecular formula C6H14
and
exemplify the infrared, mass, 1H NMR and 13C NMR spectra of lower
aliphatic alkanes (non-cyclic alkanes). |
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Infrared spectra below. |
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INFRARED SPECTRA:
Apart from the significant differences in the fingerprint region at
wavenumbers 1500 to 400 cm-1, there are no other
great striking differences, but each could be identified from
its infrared spectrum.
All the absorption
bands are typical of molecules containing saturated alkyl structure and
there are no characteristic infrared absorptions due to a specific
functional group. |
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Infrared spectra above, mass spectra below. |
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MASS SPECTRA: Base ion
peaks plus m/z comments.
Hexane: m/z 57, 42 and 56 prominent
2-methylpentane: m/z 43, 42 and 71 prominent
3-methylpentane: m/z 57, 41 and 56 prominent
2,2-dimethylbutane: m/z 43, 41, 57 and 71
prominent
2,3-dimethylbutane: m/z 43, 41, 42 and 71
prominent |
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Mass spectra above, 1H NMR spectra below. |
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1H NMR SPECTRA: They can
all be distinguished by their different integrated proton ratios -
need very high resolution.
Hexane:
3 1H
δ shifts, H ratio 3:2:2 (6:4:4 in formula)
2-methylpentane:
5 1H
δ shifts, H ratio 6:3:2:2:1
3-methylpentane:
4 1H
δ shifts, H ratio 6:4:3:1
2,2-dimethylbutane: 3 1H
δ shifts, H ratio 9:3:2
2,3-dimethylbutane: 2 1H
δ shifts, H ratio 6:1 (12:2 in formula) |
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1H NMR spectra above, 13C NMR spectra below. |
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13C NMR SPECTRA: From the
number of shifts, you can't distinguish (iii) and (iv) but you can
distinguish them from (i), (ii) and (v). (i) Hexane: 3 13C
δ shifts
(ii) 2-methylpentane: 5 13C
δ shifts
(iii) 3-methylpentane: 4 13C
δ shifts
(iv) 2,2-dimethylbutane: 4 13C
δ shifts
(v) 2,3-dimethylbutane: 2 13C
δ shifts |
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13C NMR spectra above. |
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
2-methylpentane.
|
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 |
|
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 |
|
1 |
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5
creates a sextet |
|
1 |
|
5 |
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10 |
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10 |
|
5 |
|
1 |
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6
creates a septet |
1 |
|
6 |
|
15 |
|
20 |
|
15 |
|
6 |
|
1 |
Key words & phrases:: isohexane
Interpreting the proton H-1 NMR spectra of 2-methylpentane, low resolution & high resolution proton
nmr spectra of 2-methylpentane, H-1 nmr spectrum of 2-methylpentane, understanding the
hydrogen-1 nmr spectrum of 2-methylpentane, explaining the line splitting patterns in the
high resolution H-1 nmr spectra of 2-methylpentane, revising the H-1 nmr spectrum of
2-methylpentane,
proton nmr of 2-methylpentane, ppm chemical shifts of the H-1 nmr spectrum of
2-methylpentane,
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 2-methylpentane, how to work out the
number of chemically different protons in the structure of the 2-methylpentane organic
molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR
spectrum of 2-methylpentane using the n+1 rule to explain the spin - spin coupling ine
splitting in the proton nmr spectrum of 2-methylpentane deducing the nature of the protons
from the chemical shifts ppm in the H-1 nmr spectrum of 2-methylpentane
examining the 1H nmr spectrum of 2-methylpentane analysing the 1-H nmr spectrum of
2-methylpentane how do you sketch and interpret the H-1 NMR spectrum of
2-methylpentane
interpreting interpretation of the H-1 proton NMR spectrum of 2-methylpentane:
isohexane Molecular structure diagram of the
proton NMR diagram for the 1H NMR spectrum of 2-methylpentane. The proton ratio in the
1H NMR spectrum of 2-methylpentane. Deducing the number of different chemical
environments of the protons in the 2-methylpentane molecule from the 1H chemical shifts
in the hydrogen-1 NMR spectrum of 2-methylpentane. Analysing the high resolution 1H NMR
spectrum of 2-methylpentane. Analysing the low resolution 1H NMR spectrum of
2-methylpentane. You
may need to know the relative molecular mass of 2-methylpentane to deduce the molecular
formula from the proton ratio of the 1H NMR spectrum of 2-methylpentane. Revision notes
on the proton NMR spectrum of 2-methylpentane. Matching and deducing the structure of
the 2-methylpentane molecule from its hydrogen-1 NMR spectrum.
Proton NMR spectroscopy of aliphatic
alkanes,
1H NMR spectra of 2-methylpentane, an isomer of molecular formula
C6H14
How do you interpret the H-1 NMR spectrum of 2-methylpentane How to interpret
the H-1 NMR spectrum of 2-methylpentane Explanatory diagram of the chemical
shifts of the 1H H-1 proton NMR spectrum of the 2-methylpentane
molecule in terms of its molecular structure. Listing data of all the chemical shift peaks in ppm in the
proton NMR spectrum of 2-methylpentane. How to explain the H-1 NMR spectrum of
2-methylpentane. The chemical shifts and integrated values of the proton ratios in the 1-H NMR
spectrum of the 2-methylpentane molecule. How to work out the molecular
structure of the 2-methylpentane molecule from its proton NMR spectrum. The uses
and distinctive features of the proton NMR spectrum of the
2-methylpentane
molecule explained. What does the H-1 proton NMR spectrum chemical
shifts tell us about the
structure and properties of the 2-methylpentane
molecule? explaining the spin-spin proton coupling effects in the 1H
NMR spectrum of 2-methylpentane.
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 2-methylpentane
Links associated
with
2-methylpentane
The chemistry of ALKANES
revision notes INDEX
The infrared spectrum of
2-methylpentane
The mass spectrum of
2-methylpentane
The C-13 NMR spectrum of
2-methylpentane
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
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