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Interpreting the
13C NMR spectrum of
2,2-dimethylpropane
[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
13C NMR spectrum of
2,2-dimethylpropane
[updated
October 29th 2025]
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13C NMR spectrum of
C(CH3)4
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Links associated with 2,2-dimethylpropane
C-13
NMR spectroscopy - spectra index
See also
comparing the infrared, mass,
1H NMR and 13C NMR
spectra of the 3 alkane isomers of C5H12
Introductory note on the 13C NMR spectrum of 2,2-dimethylpropane
Students and teachers please note that my explanation of the
carbon-13 NMR spectrum of 2,2-dimethylpropane is designed for advanced, but
pre-university, chemistry courses.
The description does not involve
the chemical shift δ
spin-spin coupling effects for 2,2-dimethylpropane 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
2,2-dimethylpropane molecule.
The most common solvent used for investigating the C13 NMR
spectrum of compounds like 2,2-dimethylpropane, 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 - 2,2-dimethylpropane here.
2,2-dimethylpropane C5H12
 ,
,
For more
see The molecular structure and
naming of alkanes
Interpreting the C-13 NMR spectrum of 2,2-dimethylpropane
As you can see from the diagram above there are
two different 13C
chemical shift lines in the C-13 NMR spectrum of
2,2-dimethylpropane
indicating two different chemical environments of the carbon atoms.
(CH3)4C
Note:
(i) The 2 colours indicating the
2 different
13C chemical environments of the carbon atoms in
2,2-dimethylpropane. The central carbon atoms has a unique
13C
NMR chemical
shift (a).
(ii) All the carbons of the four methyl groups are
in an
13C identical chemical environment due to the high symmetry of the
molecule i.e. >C< tetrahedral bond network from the central carbon
atom to the methyl groups of 2,2-dimethylpropane,
13C
NMR chemical
shift (b).
The carbon-13 NMR spectra a provides direct evidence of
only 2 different
13C carbon atom environments in the 2,2-dimethylpropane molecule from 2 different chemical
shifts (ppm).
Key
points about the 13C NMR spectrum of 2,2-dimethylpropane
The ¹³C NMR spectrum of
2,2-dimethylpropane shows only two distinct carbon environments due
to its high symmetry: one for the central quaternary carbon and one
for the equivalent methyl carbons.
Key Features of the ¹³C NMR Spectrum
2,2-Dimethylpropane (neopentane, C5H12) is a highly
symmetrical alkane with four methyl groups bonded to a central carbon. This
leads to:
- Only two signals in the ¹³C NMR spectrum.
- Quaternary carbon (central C) appears downfield due to
deshielding.
- Methyl carbons appear upfield due to shielding and
electron density.
¹³C Chemical Shifts and Assignments
| Chemical Shift (δ, ppm) |
Carbon Type |
Environment |
Notes |
| ~27,
28 ppm |
CH3 (methyl) |
Four equivalent methyl groups |
Shielded, upfield signal |
| ~50?,
33 ppm |
C (quaternary) |
Central carbon bonded to 4 CH3 |
Deshielded due to electron withdrawal |
Sources:
https://sdbs.db.aist.go.jp/
diagram 13C
δ ppm spectral database of
organic compounds
Common Misconceptions
- Expecting five signals for five carbons: Symmetry
reduces the number of unique environments to two.
- Confusing quaternary carbon shift: Students may expect
it to appear upfield like methyls; it’s actually more deshielded.
- Assuming splitting patterns: ¹³C NMR spectra are
typically proton-decoupled in educational contexts—no splitting is observed.
Exam Revision Tips
For A-levels (AQA, Edexcel, OCR, WJEC, CCEA), CIE, IB, and US AP
Chemistry:
- Count unique carbon environments, not atoms: Use
symmetry to determine how many signals to expect.
- Know typical chemical shift ranges:
- Methyl (CH3): ~10–30 ppm
- Quaternary alkyl C: ~30–60 ppm
- Use ¹³C NMR to distinguish isomers: Compare spectra of
pentane, 2-methylbutane, and 2,2-dimethylpropane—more branching often means
fewer signals.
- Link shifts to electron density: More substituted or
electron-deficient carbons appear downfield.
- Practice with decoupled spectra: Most school-level
spectra are proton-decoupled—focus on chemical shifts and count of signals.
Tips for spotting
equivalent methyl group carbons in 13C NMR
e.g. 4 methyl groups on C2 of 2,2-dimethypropane
- 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, that’s a
strong hint they’re equivalent, here in 2,2-dimethylpropane we have 4
equivalent carbon atoms.
- Compare with isomers:
Try contrasting with
2,2-dimethylpropane with isomeric
3-methylbutane, 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.
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Comparing the infrared, mass, 1H NMR and 13C NMR
spectra of the 3 alkane isomers of C5H12
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 pentane,
2-methylbutane and 2,2-dimethylpropane image sizes. |
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 |
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Comparing the
infrared
spectra of pentane, 2-methylbutane and 2,2-dimethylpropane
Pentane,
2-methylbutane and 2,2-dimethylpropane
are structural isomers of molecular formula C5H12
Pentane,
2-methylbutane and 2,2-dimethylpropane
exemplify infrared spectra of the alkane homologous series CnH2n+2
hydrocarbon
molecules, where n = 5 |
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INFRARED SPECTRA
(above): There are, as expected, differences in the fingerprint region at
wavenumbers 1500 to 400 cm-1, but there is no
specific infrared absorption band for a functional group. The
infrared spectra of pentane and 2-methylbutane seem very
similar, but that of 2,2-dimethylpropane seems much simpler. |
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 |
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Comparing the
mass
spectra of pentane, 2-methylbutane and 2,2-dimethylpropane
Pentane,
2-methylbutane and 2,2-dimethylpropane
are structural isomers of molecular formula C5H12
Pentane,
2-methylbutane and 2,2-dimethylpropane
exemplify the mass spectra of the alkane series CnH2n+2
hydrocarbon
molecules, where n = 5 |
|
MASS SPECTRA (above):
All three hydrocarbons show some similarities in their mass
spectra e.g. m/z ions 27 to 29 for [C2Hx]+
(x = 2 and 4). The molecular ion peaks will
be the same for all three isomers (m/z 72),
but it is very tiny for 2,2-dimethypropane. The pattern ratios
for m/z 39 to 43 are similar for pentane and 2-methylbutane, but
m/z 42 and 43 ions are almost absent from the
2,2-dimethylpropane spectrum. The base peak ion for pentane is
m/z 43, but for 2-methylbutane and 2,2-dimethylpropane it is m/z
57. |
 |
 |
 |
Comparing the
1H proton NMR
spectra of pentane, 2-methylbutane and 2,2-dimethylpropane
Pentane,
2-methylbutane and 2,2-dimethylpropane
are structural isomers of molecular formula C5H12
Pentane,
2-methylbutane and 2,2-dimethylpropane exemplify the 1H proton NMR spectra of the alkane
homologous series CnH2n+2
hydrocarbon
molecules where, n = 5 |
|
1H NMR SPECTRA (above): The 1H NMR spectra of
all three molecules give different proton ratios for the
different 1H chemical environments i.e. pentane's
proton ratio is 3:2:1 (from 6:4:2 H's in the molecule).
2-methylbutane's proton ratio is 6:1:2:3 and
2,2-dimethylpropane's doesn't have a proton ratio, all hydrogen
atoms are equivalent. This means all three isomeric C5H12
hydrocarbons can be distinguished from their 1H NMR spectra. |
 |
 |
 |
Comparing the
carbon-13 NMR
spectra of pentane, 2-methylbutane and 2,2-dimethylpropane
Pentane,
2-methylbutane and 2,2-dimethylpropane
are structural isomers of molecular formula C5H12
Pentane,
2-methylbutane and 2,2-dimethylpropane exemplify the carbon-13 NMR spectra of
members of the alkane homologous series CnH2n+2
hydrocarbon
molecules, where n = 5 |
|
13C NMR SPECTRA
(above): The
13C NMR spectra of the three molecules show different numbers of
carbon-13 chemical environments i.e different numbers of 13C NMR
resonance lines. So, pentane gives three 13C chemical
shifts,
2-methylbutane four and 2,2-dimethylpropane two. This means all
three isomeric C5H12 hydrocarbons can be
distinguished from their 13C NMR spectra. |
Key words & phrases:
dimethylpropane neopentane
Interpreting the C-13 NMR spectra of 2,2-dimethylpropane, C-13 nmr spectrum of
2,2-dimethylpropane, understanding the
carbon-13 nmr spectrum of 2,2-dimethylpropane, explaining the line pattern in the high
resolution C-13 nmr spectra of 2,2-dimethylpropane, revising the C-13 nmr spectrum of
2,2-dimethylpropane, ppm
chemical shifts of the C-13 nmr spectrum of 2,2-dimethylpropane, how to construct the diagram of
the C-13 nmr spectrum of 2,2-dimethylpropane, how to analyse the chemical shifts in the
carbon-13 NMR spectrum of 2,2-dimethylpropane deducing the chemical environment of all the
carbon atoms in 2,2-dimethylpropane examining the c13 nmr spectrum of
2,2-dimethylpropane analysing the
13-c nmr spectrum of 2,2-dimethylpropane how do you sketch and interpret the
C-13 NMR spectrum of 2,2-dimethylpropane neopentane
dimethylpropane Molecular structure diagram of the
carbon-13 NMR diagram for the 13C NMR spectrum of 2,2-dimethylpropane. Deducing the number
of different chemical environments of the carbon atoms in the
2,2-dimethylpropane molecule
from the 13C chemical shifts in the carbon-13 NMR spectrum of
2,2-dimethylpropane. Revision
notes on the carbon-13 NMR spectrum of 2,2-dimethylpropane. Matching and deducing the
structure of the 2,2-dimethylpropane molecule from its 13C NMR spectrum.
Carbon-13 NMR spectroscopy of type,
13C NMR spectra of 2,2-dimethylpropane, an isomer of molecular formula C5H12
How do you interpret the chemical shifts of the C-13 NMR spectrum
of 2,2-dimethylpropane How to interpret the C-13 NMR spectrum of
2,2-dimethylpropane Explanatory diagram of the 13C C-13 carbon-13 NMR spectrum of the number of different carbon atom
environments in the 2,2-dimethylpropane molecule from its carbon-13 NMR spectrum to
help work out the molecular structure of the
2,2-dimethylpropane molecule? The uses
and distinctive features of the carbon-13 NMR spectrum of the
2,2-dimethylpropane
molecule explained. What do the number and values of the chemical
shifts from the c-13 carbon-13 NMR spectrum tell us about the
2,2-dimethylpropane
molecule? explaining the decoupled carbon-13 NMR spectrum of
2,2-dimethylpropane
with a detailed interpretation diagram of all the C-13 chemical shifts and
intensities
Links associated
with
2,2-dimethylpropane
The chemistry of ALKANES
revision notes INDEX
The infrared spectrum for 2,2-dimethylpropane
The mass spectrum for 2,2-dimethylpropane
The H-1 NMR spectrum for 2,2-dimethylpropane
C-13
NMR spectroscopy index
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