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Interpreting
1H NMR spectrum of 2,3-dimethylpentane
[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 & AP honors chemistry courses: Molecular
spectroscopy - analysing
1H NMR spectrum of
2,3-dimethylpentane
[updated
31st 2025]
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brown
Re-edit 1H NMR spectrum of
CH3CH(CH3)CH(CH3)CH2CH3
This is a BIG
website, PLEASE take time to explore it
Links
associated with 2,3-dimethylpentane
H-1 proton NMR spectroscopy -
spectra index
See also
comparing the
1H NMR and 13C NMR spectra of the nine alkane structural isomers of C7H16
Introductory note on the 1H NMR spectra of 2,3-dimethylpentane
Students and teachers please note my explanation of the
proton NMR spectrum of 2,3-dimethylpentane is designed for advanced, but
pre-university, chemistry courses.
The chemical shift
δ splitting pattern effects for
2,3-dimethylpentane 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
2,3-dimethylpentane 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 2,3-dimethylpentane molecule.
The most common solvent used for investigating the 1H NMR
spectrum of compounds like 2,3-dimethylpentane, 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 - 2,3-dimethylpentane here.
The chemical shifts quoted in ppm on the diagram of
the H-1 NMR spectrum of 2,3-dimethylpentane 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 2,3-dimethylpentane molecule.
2,3-dimethylpentane C7H16
For more
see
The molecular structure,
classification and
naming of alkanes
Interpreting the
H-1 NMR spectrum of
2,3-dimethylpentane
(CH3)2CHCH(CH3)CH2CH3
From the structural formula, you might expect
the 16 protons to occupy 6 different chemical environments in
the ratio 6:1:1:3:2:3.
Apparently this is not the case, and protons
a1 and
a2
are not equivalent despite the fact that the two methyl
groups are attached to the same CH group carbon atom, but giving two
different chemical shifts.
Not only that, the two protons
e1
an
e2,
on the same carbon atom, are also not equivalent,
giving two different chemical shifts.
So, is this due to the effect of the
chiral
carbon atom of proton
c giving rise to
R/S isomers with different sets of chemical shifts?
This means
there are theoretically 7 different 1H NMR chemical shifts
(but are identical to 2 d.p.)
I think this is a university level
situation, so I'm leaving it at that, as My advanced organic
chemistry notes are designed for pre-university students.
I would value other opinions on interpreting the
1H
NMR spectrum of 2,3-dimethylpentane.
Key
points about the 1H NMR spectrum of 2,3-dimethylpentane
The
1H
NMR spectrum of 2,3-dimethylpentane is very complicated and, in
high resolution, can show up to 7 distinct carbon environments
due to molecular symmetry, all appearing in the alkyl region (δ
~0.8–1.3 ppm).
C3 is chiral and causes
complications in interpreting the 1H NMR spectrum of
2,3-dimethylpentane.
Overview:
¹H NMR of 2,3-dimethylpentane
2,3-dimethylpentane (C7H16)
is a highly unsymmetrical branched alkane, leading
to more unique proton environments than expected
for a seven-carbon molecule.
Its ¹H NMR spectrum is a classic
example of how lack of symmetry increases proton signal
count.
Table: ¹H NMR Chemical Shifts,
Origins, and Integration
A simplified interpretation, 3 main
groups of very close chemical shifts
- but, in reality, it is too complicated for pre-university students,
see the 1H NMR chemical shift diagram below the table.
| δ
(ppm) |
Proton Type |
Environment |
Integration |
Splitting |
Notes |
| ~0.90 |
CH3
(terminal methyls) |
C–CH3
(methyl on C1 and C5) |
6H |
Triplet |
Coupled to
adjacent CH2 |
| ~1.00 |
CH3
(on C2 and C3) |
(CH3)2–CH–CH(CH3)2
(gem-dimethyl groups) |
12H |
Singlet |
Equivalent due to
symmetry |
| ~1.20 |
CH (methine
protons) |
Central CH on C2
and C3 |
2H |
Multiplet |
Coupled to
adjacent CH3
and CH2
groups |
BUT, high resolution 1H NMR
chemical shift information for 2,3-dimethylpentane is shown on the left
(repeated) diagram.
The seven, instead of six chemical
shifts is due to the asymmetry of the 1H proton fields caused
by the chiral carbon C3.
The C2 methyl groups are not
equivalent.
Sources: SpectraBase and
https://sdbs.db.aist.go.jp/
diagram 1H
δ ppm
spectral database of organic compounds
Common
Misconceptions in Exams
- Expecting 7 signals for 7
carbons: Symmetry
reduces the number of unique proton environments - but here 7
signals do actually appear due to a chiral carbon increasing the
asymmetry of the molecule.
- Misidentifying singlets:
The 12H singlet from the gem-dimethyl groups is often mistaken for
overlapping peaks.
- Overinterpreting splitting:
In branched alkanes, splitting patterns can be complex or collapse
due to equivalent neighbours, not so here!
- Assuming downfield shifts:
No electronegative atoms or π systems are present, so all signals
are upfield (δ < 1.5 ppm).
Exam
Revision Tips
(AQA, Edexcel, OCR, WJEC, CCEA, CIE, IB, AP)
- Count environments, not
atoms: Use symmetry to
predict the number of signals.
- Use integration ratios:
Simpler proton ratios are a strong clue for equivalent methyl
groups, not so here.
- Link splitting to
neighbours: Apply the
n+1 rule, but be cautious with overlapping or equivalent groups,
much too complex here.
- Sketch the structure:
Visualizing the molecule helps identify equivalent protons.
- Comparing C7H16 isomers:
Practice distinguishing 2,3-dimethylpentane from 2,4-dimethylpentane or
n-heptane by signal count and integration, note the differences in
number of 1H signals due to equivalence or
non-equivalence of methyl groups (see below).
- Interpretation:
Be prepared to deduce structure from spectra without labels—practice
assigning peaks from scratch.
Tips for
spotting equivalent methyl group protons in 1H NMR
e.g. 4 methyl groups in 2,2-dimethylbutane
- Check for identical
attachments: If two
or more methyl groups are bonded to the same carbon and that carbon is not
chiral, they are usually equivalent.
- Look for symmetry:
Even partial symmetry can lead to
equivalence.
- Use integration clues:
If two methyl groups give a single peak with integration of 6H (3
gives 9H), that's a strong hint they are equivalent.
- Compare with isomers:
Try contrasting with
2,2-dimethylpentane
with isomeric 3-methylpentane, where methyl
proton environments differ more clearly.
- Counting all 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).
|
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 |
|
Comparing the
1H NMR and 13C NMR spectra of the nine alkane structural isomers of C7H16
You can distinguish all 9 isomers from a data combination of their number of
1H NMR
chemical shifts,
and their resulting integrated 1H proton ratios, plus, their number of
13C
chemical shifts. |
|
Name of the alkane structural isomer of molecular
formula C7H16 |
Abbreviated structural formulae
of the nine isomers of molecular formula C7H16 (interpretation complications with 3-methylhexane and
2,3-dimethylpentane because they exhibit R/S isomerism due to a
chiral carbon) |
Skeletal formula of the
nine
alkane isomers of
molecular formula C7H16 |
Number of 1H NMR chemical shifts (δ) and
proton ratio (links
to spectrum) |
Number of 13C chemical shifts (δ)
(links
to spectrum) |
|
heptane |
 |
 |
4 δ: proton ratio: 3:2:2:1 (6:4:4:2 in the molecule) |
4 δ shifts |
|
2-methylhexane |
 |
 |
6 δ: proton ratio :
6:3:2:2:2:1 |
6 δ shifts |
|
3-methylhexane |
 |
 |
7 δ: proton ratio:
3:3:3:2:2:2:1 (simplification) ! |
7
δ shifts |
|
3-ethylpentane |
 |
 |
3 δ: proton ratio:
9:6:1 |
3 δ
shifts |
|
2,2-dimethylpentane |
 |
 |
4 δ: proton ratio:
9:3:2:2 |
5 δ shifts |
|
2,3-dimethylpentane |
|
|
6 δ: proton ratio:
6:3:3:2:1:1 (simplification) ! |
6 δ
shifts (simplification) !!! |
|
2,4-dimethylpentane |
 |
 |
3 δ: proton ratio:
12:2:2 |
3 δ
shifts |
|
3,3-dimethylpentane |
 |
 |
3 δ: proton ratio:
3:3:2 (6:4:4 in the molecule) |
4 δ
shifts |
|
2,2,3-trimethylbutane |
 |
 |
3 δ: proton ratio:
9:6:1 |
4 δ shifts |
Key words & phrases:
C7H16
Interpreting the proton H-1 NMR spectra of 2,3-dimethylpentane, low resolution & high resolution proton
nmr spectra of 2,3-dimethylpentane, H-1 nmr spectrum of 2,3-dimethylpentane, understanding the
hydrogen-1 nmr spectrum of 2,3-dimethylpentane, explaining the line splitting patterns in the
high resolution H-1 nmr spectra of 2,3-dimethylpentane, revising the H-1 nmr spectrum of
2,3-dimethylpentane,
proton nmr of 2,3-dimethylpentane, ppm chemical shifts of the H-1 nmr spectrum of
2,3-dimethylpentane,
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 2,3-dimethylpentane, how to work out the
number of chemically different protons in the structure of the
2,3-dimethylpentane organic
molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR
spectrum of 2,3-dimethylpentane using the n+1 rule to explain the spin - spin coupling
spin
splitting in the proton nmr spectrum of 2,3-dimethylpentane deducing the nature of the protons
from the chemical shifts ppm in the H-1 nmr spectrum of 2,3-dimethylpentane
examining the 1H nmr spectrum of 2,3-dimethylpentane analysing the 1-H nmr spectrum of
2,3-dimethylpentane how do you sketch and interpret the H-1 NMR spectrum of
2,3-dimethylpentane
interpreting interpretation of the 1H proton NMR spectrum of 2,3-dimethylpentane
(CH3)2CHCH(CH3)CH2CH3
Molecular structure diagram of the
proton NMR diagram for the 1H NMR spectrum of 2,3-dimethylpentane. The proton ratio in the
1H NMR spectrum of 2,3-dimethylpentane. Deducing the number of different chemical
environments of the protons in the 2,3-dimethylpentane molecule from the 1H chemical shifts
in the hydrogen-1 NMR spectrum of 2,3-dimethylpentane. Analysing the high resolution 1H NMR
spectrum of 2,3-dimethylpentane. Analysing the low resolution 1H NMR spectrum of
2,3-dimethylpentane. You
may need to know the relative molecular mass of 2,3-dimethylpentane to deduce the molecular
formula from the proton ratio of the 1H NMR spectrum of 2,3-dimethylpentane. Revision notes
on the proton NMR spectrum of 2,3-dimethylpentane. Matching and deducing the structure of
the 2,3-dimethylpentane molecule from its hydrogen-1 NMR spectrum.
Proton NMR spectroscopy of aliphatic alkanes,
1H NMR spectra of 2,3-dimethylpentane, a structural isomer of molecular formula
C7H16
How do you interpret the H-1 NMR spectrum of
2,3-dimethylpentane How to interpret
the H-1 NMR spectrum of 2,3-dimethylpentane Explanatory diagram of the chemical
shifts of the 1H H-1 proton NMR spectrum of the
2,3-dimethylpentane
molecule in terms of its molecular structure. Listing data of all the chemical shift peaks in ppm in the
proton NMR spectrum of 2,3-dimethylpentane. How to explain the H-1 NMR spectrum of
2,3-dimethylpentane. The chemical shifts and integrated values of the proton ratios in the 1-H NMR
spectrum of the 2,3-dimethylpentane molecule. How to work out the molecular
structure of the 2,3-dimethylpentane molecule from its proton NMR spectrum. The uses
and distinctive features of the proton NMR spectrum of the
2,3-dimethylpentane
molecule explained. What does the H-1 proton NMR spectrum chemical
shifts tell us about the
structure and properties of the 2,3-dimethylpentane
molecule? explaining the spin-spin proton coupling effects in the 1H
NMR spectrum of 2,3-dimethylpentane.
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
2,3-dimethylpentane
Links associated
with
2,3-dimethylpentane
The infrared spectrum of
2,3-dimethylpentane
The mass spectrum of
2,3-dimethylpentane
The C-13 NMR spectrum of
2,3-dimethylpentane
The chemistry of ALKANES
revision notes INDEX
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
Use My Google search site box
Email doc b:
chem55555@hotmail.com
|
Infrared spectra of the isomers of C7H16
The infrared
spectrum of heptane
The
infrared spectrum of 2-methylhexane
The
infrared spectrum of 3-methylhexane
The
infrared spectrum of 3-ethylpentane
The infrared spectrum of
2,2-dimethylpentane
The infrared spectrum of
2,3-dimethylpentane
The infrared spectrum of
2,4-dimethylpentane
The infrared spectrum of
3,3-dimethylpentane
The infrared spectrum
of 2,2,3-trimethylbutane
|
Mass spectra of the isomers of C7H16
The mass
spectrum of heptane
The mass
spectrum of 2-methylhexane
The mass
spectrum of 3-methylhexane
The
mass spectrum of 3-ethylpentane
The mass spectrum of
2,2-dimethylpentane
The mass spectrum of
2,3-dimethylpentane
The mass spectrum of
2,4-dimethylpentane
The mass spectrum of
3,3-dimethylpentane
The mass
spectrum of 2,2,3-trimethylbutane
|
1H NMR spectra of the isomers of C7H16
The H-1 NMR
spectrum of heptane
The
H-1 NMR spectrum of 2-methylhexane
The
H-1 NMR spectrum of 3-methylhexane
The
H-1 NMR spectrum of 3-ethylpentane
The H-1 NMR spectrum of
2,2-dimethylpentane
The H-1 NMR spectrum of
2,3-dimethylpentane
The H-1 NMR spectrum of
2,4-dimethylpentane
The H-1 NMR spectrum of
3,3-dimethylpentane
The H-1
NMR spectrum of 2,2,3-trimethylbutane
|
13C NMR spectra of the isomers of C7H16
The C-13 NMR
spectrum of heptane
The
C-13 NMR spectrum of 2-methylhexane
The
C-13 NMR spectrum of 3-methylhexane
The
C-13 NMR spectrum of 3-ethylpentane
The C-13 NMR spectrum of
2,2-dimethylpentane
The C-13 NMR spectrum of
2,3-dimethylpentane
The C-13 NMR spectrum of
2,4-dimethylpentane
The C-13 NMR spectrum of
3,3-dimethylpentane
The
C-13 NMR spectrum of 2,2,3-trimethylbutane
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