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Interpreting the
13C NMR spectrum of
3-ethylpentane
[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
C-13 NMR spectrum of
2-ethylpentane
[updated
October 24th 2025]
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HC(CH2CH3)3
The chemistry of ALKANES and the petrochemical
industry
Links associated with 3-ethylpentane
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website, PLEASE take time to explore it
C-13
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 13C NMR spectrum of 3-ethylpentane
Students and teachers please note that my explanation of the
carbon-13 NMR spectrum of 3-ethylpentane is designed for advanced, but
pre-university, chemistry courses.
The description does not involve
the chemical shift δ
spin-spin coupling effects for 3-ethylpentane and the relative size of the carbon-13
NMR shifts does not give the ratio of the carbon atoms in the
different non-equivalent chemical environments of the 3-ethylpentane molecule.
The most common solvent used for investigating the C13 NMR
spectrum of compounds like 3-ethylpentane, is CDCl3 and other
deuterated solvents.
TMS is the acronym for tetramethylsilane, formula Si(CH3)4,
whose 13C atoms are arbitrarily given a chemical shift of 0.0
ppm. This is the 'standard' in 13C NMR spectroscopy and all other
13C resonances, called chemical shifts, are measured with
respect to the TMS, and depend on the
individual (electronic) chemical environment of the 13C atoms in
an organic molecule - 3-ethylpentane here.
3-ethylpentane
CH(CH2CH3)3
For more
see
The molecular structure,
classification and
naming of alkanes
Interpreting the C-13 NMR spectrum of 3-ethylpentane
As you can see from the diagram above there are
3 different chemical shift lines in the C-13 NMR spectrum of
3-ethylpentane
indicating 3 different chemical environments of the carbon atoms.
(CH3CH2)3CH
(Note the 3 different colours indicating the
3 different chemical environments of the 7 carbon atoms in
3-ethylpentane).
Chemical shifts
(a) to (c) on the C-13 NMR
spectrum diagram for 3-ethylpentane.
The higher symmetry of the 3-ethylpentane
molecules reduces the chemical environments of the protons
compared to seven of the other isomers of C7H16.
(see comparison table below)
(a) All three of
the -CH3 group carbon atoms are chemically equivalent to each
other, so give the same C-13 NMR shift of 11.0 ppm because they
occupy identical chemical environments.
(b) All three of
the -CH2- group carbon atoms are chemically equivalent to each
other, so give the same C-13 NMR shift of 25.2 ppm because they
occupy identical chemical environments.
(c) The only unique C-13 chemical environment is the
carbon atom of the >CH- grouping, so has a different C-13 NMR
chemical shift of 42.3 ppm.
The carbon-13 NMR spectra a provides direct evidence of
3 different carbon atom environments for the 7 carbon atoms in the
3-ethylpentane molecule,
deduced from the presence of 3 different 13C chemical
shifts (ppm).
Key points about
the 1H NMR spectrum of 2-ethylpentane
Structure of
2-Ethylpentane
The ¹³C NMR Signal
Count
| Carbon Type |
Environment |
Approx. δ (ppm) |
Equivalence |
Signal Count |
| CH3 |
Three methyl groups |
~14–15, 11.0 ppm |
Equivalent |
1 |
| CH2 |
Three methylene groups |
~22–25, 25.2 ppm |
Equivalent |
1 |
| CH |
One tertiary carbon (C3) |
~35–40, 42.3 ppm |
Unique |
1 |
Total signals = 3 — due to three equivalent ethyl
groups centered around C3.
https://sdbs.db.aist.go.jp/
diagram δ ppm spectral database of organic
compounds
Why This Is Crucial
for Exams
- Questions often ask for number of signals and
justification of equivalence.
- Recognizing symmetry and branching is
essential.
- Expect spectrum-to-structure and
structure-to-spectrum reasoning.
- Miscounting signals due to overlooked equivalence is a common trap.
- Focus on basic NMR principles and recognizing
equivalent environments.
- This example is ideal for teaching alkyl equivalence logic.
Misconceptions to
Avoid
- Assuming each carbon gives a separate signal:
Equivalent environments collapse into one signal.
- Ignoring free rotation and symmetry:
Leads to overcounting signals.
- Treating CH3 or CH2 groups as automatically unique:
Always assess connectivity and surroundings.
Revision Summary
- 3 signals in ¹³C NMR for 2-ethylpentane.
- All signals fall in the alkyl region (0–50 ppm).
- Use symmetry and branching to identify equivalence.
- ¹³C NMR spectra are proton-decoupled — no splitting.
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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 C-13 NMR spectra of
3-ethylpentane, C-13 nmr spectrum of 3-ethylpentane, understanding the
carbon-13 nmr spectrum of 3-ethylpentane, explaining the line pattern in the high
resolution C-13 nmr spectra of 3-ethylpentane, revising the C-13 nmr spectrum of
3-ethylpentane, ppm
chemical shifts of the C-13 nmr spectrum of 3-ethylpentane, how to construct the diagram of
the C-13 nmr spectrum of 3-ethylpentane, how to analyse the chemical shifts in the
carbon-13 NMR spectrum of 3-ethylpentane deducing the chemical environment of all the
carbon atoms in 3-ethylpentane examining the c13 nmr spectrum of
3-ethylpentane analysing the
13-c nmr spectrum of 3-ethylpentane how do you sketch and interpret the C-13 NMR spectrum
of 3-ethylpentane interpreting interpretation of the C-13 NMR spectrum of
3-ethylpentane
13C NMR spectrum of 3-ethylpentane
(CH3CH2)3CH CH3CH2CH(CH2CH3)CH2CH3
Molecular structure diagram of the
carbon-13 NMR diagram for the 13C NMR spectrum of 3-ethylpentane. Deducing the number
of different chemical environments of the carbon atoms in the 3-ethylpentane molecule
from the 13C chemical shifts in the carbon-13 NMR spectrum of 3-ethylpentane. Revision
notes on the carbon-13 NMR spectrum of 3-ethylpentane. Matching and deducing the
structure of the 3-ethylpentane molecule from its 13C NMR spectrum.
Carbon-13 NMR spectroscopy of aliphatic alkanes,
13C NMR spectra of 3-ethylpentane, a structural isomer of molecular formula
C7H16
How do you interpret the chemical shifts of the C-13 NMR spectrum
of 3-ethylpentane How to interpret the C-13 NMR spectrum of
3-ethylpentane Explanatory diagram of the 13C C-13 carbon-13 NMR spectrum of the number of different carbon atom
environments in the 3-ethylpentane molecule from its carbon-13 NMR spectrum to
help work out the molecular structure of the 3-ethylpentane molecule? The uses
and distinctive features of the carbon-13 NMR spectrum of the
3-ethylpentane
molecule explained. What do the number and values of the chemical
shifts from the c-13 carbon-13 NMR spectrum tell us about the
3-ethylpentane
molecule? explaining the decoupled carbon-13 NMR spectrum of
3-ethylpentane
with a detailed diagram of all the C-13 chemical shifts and
intensities
Links associated
with
3-ethylpentane
The mass spectrum of
3-eethylpentane
The
H-1 NMR spectrum of 3-ethylpentane
The infrared spectrum of
3-ethylpentane
The chemistry of ALKANES
revision notes INDEX
C-13
NMR spectroscopy index
ALL SPECTROSCOPY INDEXES
All Advanced Organic
Chemistry Notes
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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
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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
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H-1 proton NMR spectra of ALKANES
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
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C-13 carbon-13 NMR spectra
of ALKANES
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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