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Interpreting the Carbon-13 NMR spectrum of
3,3-dimethylpentane
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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 & AP honors chemistry courses: Molecular
spectroscopy - analysing
13C NMR spectrum of
3,3-dimethylpentane
[spectra updated
Mar 19th 2026 *]
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13C NMR spectrum of CH3CH2C(CH3)2CH2CH3
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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 3,3-dimethylpentane
Students and teachers please note that my explanation of the
carbon-13 NMR spectrum of 3,3-dimethylpentane is designed for advanced, but
pre-university, chemistry courses.
The description does not involve
the chemical shift δ
spin-spin coupling effects for 3,3-dimethylpentane 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
3,3-dimethylpentane molecule.
The most common solvent used for investigating the C13 NMR
spectrum of compounds like 3,3-dimethylpentane, 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 - 3,3-dimethylpentane here.
3,3-dimethylpentane C7H16
The molecular structure and
naming of alkanes
Interpreting the C-13 NMR spectrum of 3,3-dimethylpentane
As you can see from the diagram above there are
4 different chemical shift lines in the C-13 NMR spectrum of
3,3-dimethylpentane
indicating 4 different chemical environments of the carbon atoms.
CH3CH2C(CH3)2CH2CH3
(Note the 4 different colours indicating the
4 different chemical environments of the carbon atoms in
3,3-dimethylpentane).
Chemical shifts
(a) to (d) on the C-13 NMR
spectrum diagram for 3,3-dimethylpentane.
Note there are
three pairs of carbon atom in the same chemical environment
(a-a, b-b and c-c) and will therefore give the same
C-13 NMR
chemical
shift i.e. of 8.4, 33.8 and 26.2 ppm respectively.
Only the central
carbon atom
(d), has a unique chemical environment and with a
chemical shift of 32.8
Both theses
situations arise from the high symmetry of the
3,3-dimethylbutane molecule.
The carbon-13 NMR spectra a provides direct evidence of
4 different carbon atom environments for the 7 carbon atoms in the
3,3-dimethylpentane molecule,
deduced from the presence of 4 different 13C chemical
shifts (ppm).
Key points about the
13C NMR spectrum
of3,3-dimethylpentane
Overview: ¹³C NMR of 3,3-dimethylpentane
Molecular formula:
C7H16
This is a branched alkane with
seven carbon atoms, including a quaternary carbon
at position 3, so it is quite a symmetrical molecule.
¹³C
NMR Chemical Shift Table for
3,3-dimethylpentane
| Carbon Type |
Environment Description |
Approx. δ (ppm) |
Notes |
| C1, C5 (CH3) |
Terminal methyl groups |
~14, 8.4 ppm |
Equivalent due to symmetry |
| C2, C4 (CH2) |
Methylene groups adjacent to CH and
C(CH3)2 |
~22?, 33.8 ppm |
Equivalent |
| C3 (C) |
Quaternary carbon bonded to two CH3
and two CH2 |
~38, 32.8 ppm |
No attached H |
| C6, C7 (CH3) |
Methyl groups on quaternary carbon |
~29, 26.2 ppm |
Equivalent |
Total number of signals:
4
Despite having 7 carbon atoms, only 4 distinct signals appear
due to symmetry and equivalence.
https://sdbs.db.aist.go.jp/
diagram 13C
δ ppm spectral database of
organic compounds
Common
Misconceptions
| Misconception |
Clarification |
| Each carbon gives a separate
peak |
Not true—equivalent carbons
give one signal. |
| Quaternary carbons are always
downfield |
Not always—alkyl quaternary
carbons can appear upfield (~30–40 ppm). |
| More peaks = more carbons |
Not necessarily—symmetry
reduces the number of observed peaks. |
| ¹³C NMR shows splitting |
Not in proton-decoupled
spectra, which are
standard in most curricula. |
Exam Revision Tips
- Count unique carbon environments,
not total carbon atoms.
- Draw the structure
and label equivalent carbons.
- Quaternary carbons
often appear between 30–50 ppm in alkanes.
- Use symmetry
to reduce overcounting.
- No splitting
in standard ¹³C NMR spectra—focus on number and position of peaks.
- Practice with branched alkanes—they
often trip up students due to hidden symmetry.
Tips for spotting
equivalent methyl group carbons in 13C NMR
e.g. 4 methyl groups on C2 of 2,2-dimethypentane
- 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 (like in
2,2-dimethylpentane) 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 3,3-dimethylpentane with
2,2-dimethylpentane with
3-methylhexane, where methyl
carbon environments differ more clearly.
- Counting methyls as separate
signals: Leads to
overestimating the number of peaks in ¹³C 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.
Practice Question
Question:
The compound 3,3-dimethylpentane has the molecular formula C7H16.
(a) Predict the number of peaks in its ¹³C NMR spectrum.
(b) Explain why this number is less than the number of carbon atoms.
(c) Estimate the chemical shift range for the quaternary carbon.
(d) Identify the type of carbon that gives rise to the signal around 14 ppm.
Model Answer
(a)
4 peaks
(b) Due to symmetry, several carbon atoms are
chemically equivalent and give the same signal.
- C1 ≡ C5 (CH3)
- C2 ≡ C4 (CH2)
- C6 ≡ C7 (from C3 2 branched CH3)
(c) The quaternary carbon (C3) appears around 38
ppm.
(d) The signal at ~14 ppm corresponds to
terminal methyl groups (C1 and C5).
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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
3,3-dimethylpentane, C-13 nmr spectrum of 3,3-dimethylpentane, understanding the
carbon-13 nmr spectrum of 3,3-dimethylpentane, explaining the line pattern in the high
resolution C-13 nmr spectra of 3,3-dimethylpentane, revising the C-13 nmr spectrum of
3,3-dimethylpentane, ppm
chemical shifts of the C-13 nmr spectrum of 3,3-dimethylpentane, how to construct the diagram of
the C-13 nmr spectrum of 3,3-dimethylpentane, how to analyse the chemical shifts in the
carbon-13 NMR spectrum of 3,3-dimethylpentane deducing the chemical environment of all the
carbon atoms in 3,3-dimethylpentane examining the c13 nmr spectrum of
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of 3,3-dimethylpentane interpreting interpretation of the C-13 NMR spectrum of
3,3-dimethylpentane
13C NMR spectrum of 3,3-dimethylpentane
CH3CH2C(CH3)2CH2CH3 Molecular structure diagram of the
carbon-13 NMR diagram for the 13C NMR spectrum of 3,3-dimethylpentane. Deducing the number
of different chemical environments of the carbon atoms in the
3,3-dimethylpentane molecule
from the 13C chemical shifts in the carbon-13 NMR spectrum of
3,3-dimethylpentane. Revision
notes on the carbon-13 NMR spectrum of 3,3-dimethylpentane. Matching and deducing the
structure of the 3,3-dimethylpentane molecule from its 13C NMR spectrum.
Carbon-13 NMR spectroscopy of aliphatic alkanes,
13C NMR spectra of 3,3-dimethylpentane, a structural isomer of molecular formula
C7H16
How do you interpret the chemical shifts of the C-13 NMR spectrum
of 3,3-dimethylpentane How to interpret the C-13 NMR spectrum of
3,3-dimethylpentane Explanatory diagram of the 13C C-13 carbon-13 NMR spectrum of the number of different carbon atom
environments in the 3,3-dimethylpentane molecule from its carbon-13 NMR spectrum to
help work out the molecular structure of the
3,3-dimethylpentane molecule? The uses
and distinctive features of the carbon-13 NMR spectrum of the
3,3-dimethylpentane
molecule explained. What do the number and values of the chemical
shifts from the c-13 carbon-13 NMR spectrum tell us about the
3,3-dimethylpentane
molecule? explaining the decoupled carbon-13 NMR spectrum of
3,3-dimethylpentane
with a detailed interpretation diagram of all the C-13 chemical shifts and
intensities
Links associated
with
3,3-dimethylpentane
The infrared spectrum of
3,3-dimethylpentane
The mass spectrum of
3,3-dimethylpentane
The H-1 NMR spectrum of
3,3-dimethylpentane
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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