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Interpreting the
13C NMR spectrum of
2-methylhexane
[Author
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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
C-13 NMR spectrum of
2-methylhexane
[spectra
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CH3CH2CH2CH2CH(CH3)2
Links associated
with 2-methylhexane
The chemistry of ALKANES and the petrochemical
industry
This is a BIG
website, you need to 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 2-methylhexane
Students and teachers please note that my explanation of the
carbon-13 NMR spectrum of 2-methylhexane is designed for advanced, but
pre-university, chemistry courses.
The description does not involve
the chemical shift δ
spin-spin coupling effects for 2-methylhexane 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 2-methylhexane molecule.
The most common solvent used for investigating the C13 NMR
spectrum of compounds like 2-methylhexane, 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 shifts, called chemical shifts, depend on the
individual (electronic) chemical environment of the 13C atoms in
an organic molecule - 2-methylhexane here.
2-methylhexane C7H16
The molecular structure and
naming of alkanes
Interpreting the C-13 NMR spectrum of 2-methylhexane
As you can see from the diagram above there are
6 different chemical shift lines in the C-13 NMR spectrum of
2-methylhexane
indicating 6 different chemical environments of the carbon atoms.
(CH3)2CHCH2CH2CH2CH3
(Note the 6 colours indicating the
6 different chemical environments of the 7 carbon atoms in
2-methylhexane).
Chemical shifts
(a) to (f) on the C-13 NMR
spectrum diagram for 2-methylhexane.
The carbon atoms of the C(CH3)2
methyl groups are equivalent to each other i.e they give
an identical chemical shift
a (22.7 ppm) and exist in identical chemical
environments.
Theoretically, the other five carbon atoms are
in different chemical environments, despite the similarity in
disposition e.g. the CH2 groups.
The carbon-13 NMR spectra a provides direct evidence of
6 different carbon atom environments for the 7 carbon atoms in the
2-methylhexane molecule,
deduced from the presence of 6 different 13C chemical
shifts (ppm).
Summary of the ¹³C
NMR Spectrum of 2-Methylhexane
Here’s the refined breakdown of the six
unique carbon environments in 2-methylhexane,
and all appearing in the alkyl region (δ
~14–40 ppm):
| Chemical Shift (δ, ppm) |
Carbon Type |
Environment |
Notes |
| ~14,
14.2 ppm |
CH3 |
Terminal methyl (–CH3) |
Least deshielded; far from branching |
| ~22,
22.7 ppm |
2 x CH3 |
Two equivalent methyls on C-2 (–C(CH3)2) |
One signal for both methyls |
| ~27,
23.1 ppm |
CH2 |
Internal methylene |
Slightly deshielded by adjacent CH2 |
| ~30,
29.9 ppm |
CH2 |
Near branch point |
More deshielded due to branching |
| ~36,
28.2 ppm |
CH |
Methine (–CH–) at branch |
Tertiary carbon; most deshielded CH |
| ~39,
39.0 ppm |
CH2 |
Adjacent to methine |
Downfield due to proximity to tertiary
carbon |
Why Only Six
Signals?
- Symmetry and equivalence:
The two methyl groups on C-2 are in identical environments — same
connectivity, same spatial surroundings — so they resonate at the same
chemical shift.
- No quaternary carbon:
All carbons in 2-methylhexane are protonated (CH3, CH2,
CH), so no silent quaternary carbon appears.
Common
Misconceptions in ¹³C NMR
- Expecting one signal per carbon
atom: Equivalent carbons give
a single peak.
- Misidentifying methyl equivalence:
Students may assume all CH3
groups are unique without checking symmetry.
- Expecting splitting:
Standard ¹³C spectra are proton-decoupled — no splitting is observed.
Exam Revision Tips
(AQA, Edexcel, OCR, WJEC, CCEA, CIE, IB, AP)
What to Focus On
- Signal count:
Reflects number of unique carbon environments, not total carbon atoms.
- Chemical shift ranges:
- Alkyl: 0–50 ppm
- Alkene/aromatic: 100–160 ppm
- Carbonyl: 160–220 ppm
Strategy Tips
- Draw and label:
Identify equivalent carbons before predicting signal count.
- Compare isomers:
Practice with hexane, 2-methylhexane, and 3-methylhexane.
- Use symmetry:
Helps reduce complexity and predict correct number of signals.
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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
2-methylhexane, C-13 nmr spectrum of 2-methylhexane, understanding the
carbon-13 nmr spectrum of 2-methylhexane, explaining the line pattern in the high
resolution C-13 nmr spectra of 2-methylhexane, revising the C-13 nmr spectrum of
2-methylhexane, ppm
chemical shifts of the C-13 nmr spectrum of 2-methylhexane, how to construct the diagram of
the C-13 nmr spectrum of 2-methylhexane, how to analyse the chemical shifts in the
carbon-13 NMR spectrum of 2-methylhexane deducing the chemical environment of all the
carbon atoms in 2-methylhexane examining the c13 nmr spectrum of
2-methylhexane analysing the
13-c nmr spectrum of 2-methylhexane how do you sketch and interpret the C-13 NMR spectrum
of 2-methylhexane interpreting interpretation of the C-13 NMR spectrum of
2-methylhexane
13C NMR spectrum of 2-methylhexane
(CH3)2CHCH2CH2CH2CH3 Molecular structure diagram of the
carbon-13 NMR diagram for the 13C NMR spectrum of 2-methylhexane. Deducing the number
of different chemical environments of the carbon atoms in the 2-methylhexane molecule
from the 13C chemical shifts in the carbon-13 NMR spectrum of 2-methylhexane. Revision
notes on the carbon-13 NMR spectrum of 2-methylhexane. Matching and deducing the
structure of the 2-methylhexane molecule from its 13C NMR spectrum.
Carbon-13 NMR spectroscopy of aliphatic alkanes,
13C NMR spectra of 2-methylhexane, a structural isomer of molecular formula C7H16
How do you interpret the chemical shifts of the C-13 NMR spectrum
of 2-methylhexane How to interpret the C-13 NMR spectrum of
2-methylhexane Explanatory diagram of the 13C C-13 carbon-13 NMR spectrum of the number of different carbon atom
environments in the 2-methylhexane molecule from its carbon-13 NMR spectrum to
help work out the molecular structure of the 2-methylhexane molecule? The uses
and distinctive features of the carbon-13 NMR spectrum of the
2-methylhexane
molecule explained. What do the number and values of the chemical
shifts from the c-13 carbon-13 NMR spectrum tell us about the
2-methylhexane
molecule? explaining the decoupled carbon-13 NMR spectrum of
2-methylhexane
with a detailed diagram of all the C-13 chemical shifts and
intensities
Links associated
with
2-methylhexane
The
infrared spectrum of 2-methylhexane
The mass
spectrum of 2-methyhexane
The
H-1 NMR spectrum of 2-methylhexane
The chemistry of ALKANES
revision notes INDEX
C-13
NMR spectroscopy index
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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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