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Interpreting infrared
spectrum of 2,2-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 and AP honors chemistry courses: Molecular
spectroscopy - analysing the
infrared spectrum of
2,2-dimethyl pentane
[updated
October 29th 2025]
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CH3CH2CH2C(CH3)3
Links associated with 2,2-dimethylpentane
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Infrared 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 infrared spectrum of 2,2-dimethylpentane
Students and teachers please note
my explanation of the infrared
spectrum of 2,2-dimethylpentane is designed
for advanced, but pre-university, chemistry courses.
Based in
the infrared spectrum diagram for 2,2-dimethylpentane, only some of the most
prominent peaks for particular bond vibrations are discussed,
particularly if 2,2-dimethylpentane has a functional group with a particular
characteristic wavenumber peak.
The infrared spectrum of
2,2-dimethylpentane is
unique and the whole, or selected wavenumbers, can be used to
fingerprint its identity, sometimes analysing a mixture
containing 2,2-dimethylpentane or following its change of concentration in a
reaction.
Spectra obtained from a liquid film of 2,2-dimethylpentane. The right-hand part of the of the
infrared spectrum of 2,2-dimethylpentane, wavenumbers
~1500 to 400
cm-1 is considered the fingerprint region for the
identification of 2,2-dimethylpentane and most organic compounds. It is due to a unique set
of complex overlapping vibrations of the atoms of the molecule of
2,2-dimethylpentane.
2,2-dimethylpentane C7H16
The molecular structure and
naming of alkanes
Interpretation of
the infrared spectrum of 2,2-dimethylpentane
The most prominent infrared absorption lines of
2,2-dimethylpentane
Strong C-H stretching vibration absorptions at
wavenumbers 2940 to 2880 cm-1 for the CH2 and
CH3 groups in 2,2-dimethypentane.
Several strong C-H deformation vibration absorptions
at wavenumbers 1480 to 1365 cm-1 for the CH2
and CH3 groups in 2,2-dimethypentane.
Several strong C-C skeletal vibration
absorptions associated with a C-(CH3)3
group occur at wavenumbers 750 to 720 and 1255 to 1200 cm-1.
There are no specific characteristic lines for
alkanes like 2,2-dimethylpentane because C-C and C-H vibrations are common to so
many organic molecules and alkanes like octane have no functional
group that gives a characteristic vibration.
The absence of other specific functional group bands
will show that a particular functional group is absent from the
2,2-dimethylpentane
molecular
structure.
Key
points about the infrared spectrum of 2,2-dimethypentane
2,2-Dimethylpentane shows a typical
alkane IR spectrum with no functional group peaks above 3000 cm⁻¹. Key
absorptions include C–H stretches and bends, with a prominent fingerprint
region.
Misconceptions often arise from
overinterpreting this region or expecting functional group signals.
Key IR Features of
2,2-Dimethylpentane
2,2-Dimethylpentane is a saturated, branched alkane (C7H16)
with no polar functional groups. Its IR spectrum reflects this simplicity:
| Wavenumber (cm⁻¹) |
Bond Type |
Vibration Mode |
Notes |
| ~2950–2850 |
C–H (sp³) stretch |
Asymmetric & symmetric |
Multiple peaks due to
methyl/methylene groups |
| ~1470–1450 |
CH2 bend |
Scissoring |
Often appears as a doublet |
| ~1375–1365 |
CH3
bend |
Symmetric deformation |
Methyl group signature |
| < 1300 |
C–C and C–H bends |
Various |
Fingerprint region, complex but
non-diagnostic |
Sources: NIST WebBook, MolInstincts IR database
Common
Misconceptions in IR Interpretation
- Expecting functional group peaks: Students may
mistakenly look for O–H, C=O, or C≡C peaks in simple alkanes.
- Overinterpreting the fingerprint region: Below 1500
cm⁻¹, peaks are molecule-specific but not easily assignable without
reference spectra.
- Confusing sp² and sp³ C–H stretches: Alkanes show sp³
C–H stretches below 3000 cm⁻¹; sp² stretches (alkenes/aromatics) appear
above 3000 cm⁻¹.
Exam Revision Tips
(AQA, Edexcel, OCR, WJEC, CCEA, CIE, IB, AP)
- Know your regions: Functional group region (>1500 cm⁻¹)
versus fingerprint region (<1500 cm⁻¹).
- Link structure to spectrum: For branched alkanes like
2,2-dimethylpentane, expect multiple C–H stretch peaks due to different
environments.
- Use elimination: Absence of strong peaks (e.g. no O–H
~3300 cm⁻¹ or C=O ~1700 cm⁻¹) helps rule out several functional groups.
- Practice with reference spectra: Familiarity with
typical alkane spectra aids quick recognition.
- Watch for distractors: Some exam questions include
spectra with overlapping peaks—focus on the most diagnostic regions.
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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:
formula image and diagram explaining the infrared spectrum
of 2,2-dimethylpentane, complete infrared absorption spectrum of
2,2-dimethylpentane, comparative spectra of
2,2-dimethylpentane, prominent peaks/troughs for identifying functional groups in the infrared spectrum of
2,2-dimethylpentane,
important wavenumber values in cm-1 for peaks/troughs in the infrared spectrum
of 2,2-dimethylpentane, revision of infrared spectroscopy of 2,2-dimethylpentane, fingerprint region analysis of
2,2-dimethylpentane, how to identify 2,2-dimethylpentane from its infrared spectrum, identifying organic
compounds like 2,2-dimethylpentane from their infrared spectrum,
how to analyse the absorption bands in the infrared spectrum of
2,2-dimethylpentane detection of no functional groups in the
2,2-dimethylpentane molecule example of the infrared spectrum of a
molecule like 2,2-dimethylpentane with no functional group
interpreting interpretation of the infrared spectrum of
2,2-dimethylpentane shows presence
of no functional groups
(CH3)3CCH2CH2CH3 Diagram of absorption of wavenumber
peaks in the infrared spectrum of 2,2-dimethylpentane. Characteristic peak wavenumbers in the infrared
spectrum of 2,2-dimethylpentane. Finger print identification pattern using the infrared
spectrum of 2,2-dimethylpentane. Revision notes on the infrared spectrum of
2,2-dimethylpentane. Matching
and deducing the structure of the 2,2-dimethylpentane molecule from its infrared
spectrum. Infrared spectroscopy of aliphatic alkanes, infrared spectra of
2,2-dimethylpentane, a structural isomer of molecular formula C7H16 How do you interpret the infrared absorption spectrum of
2,2-dimethylpentane How
to interpret the infrared spectrum of 2,2-dimethylpentane Explanatory diagram of the
infrared spectrum of the 2,2-dimethylpentane molecule in terms of its molecular
structure. Listing data of the prominent main wavenumber peaks
troughs in the infrared spectrum of 2,2-dimethylpentane. How to explain the infrared
spectrum of 2,2-dimethylpentane. Use of the infrared spectrum of
2,2-dimethylpentane, identification
of 2,2-dimethylpentane from its infrared spectrum - fingerprint wavenumber pattern
to identify the 2,2-dimethylpentane molecule. The uses of the infrared spectrum of
the 2,2-dimethylpentane molecule. The distinctive features of the infrared spectrum
of the 2,2-dimethylpentane molecule explained interpretation diagram explaining the
peaks-trough of the transmittance of the infrared spectrum of
2,2-dimethylpentane
what does the infrared spectrum tell you about the structure and
properties of the 2,2-dimethylpentane molecule? How is infrared spectrum of
2,2-dimethylpentane used
to identify 2,2-dimethylpentane?
Links associated with 2,2-dimethylpentane
The mass spectrum of
2,2-dimethylpentane
The H-1 NMR spectrum of
2,2-dimethylpentane
The C-13 NMR spectrum of
2,2-dimethylpentane
The chemistry of ALKANES
revision notes INDEX
Infrared 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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