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Interpreting and
explaining the infrared
spectrum of heptane
[Author
©
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 analysis of
heptane
[spectra page updated
Mar 24th 2026 *]
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infrared spectrum
CH3(CH2)5CH3
Links associated with heptane
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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 heptane
Students and teachers please note
my explanation of the infrared
spectrum of heptane is designed
for advanced, but pre-university, chemistry courses.
Based in
the infrared spectrum diagram for heptane, only some of the most
prominent peaks for particular bond vibrations are discussed,
particularly if heptane has a functional group with a particular
characteristic wavenumber peak.
The infrared spectrum of
heptane is
unique and the whole, or selected wavenumbers, can be used to
fingerprint its identity, sometimes analysing a mixture
containing heptane or following its change of concentration in a
reaction.
Spectra obtained from a liquid film of heptane. The right-hand part of the of the
infrared spectrum of heptane, wavenumbers
~1500 to 400
cm-1 is considered the fingerprint region for the
identification of heptane and most organic compounds. It is due to a unique set
of complex overlapping vibrations of the atoms of the molecule of heptane.
Heptane,
C7H16 , CH3(CH2)5CH3
,
,
an alkane
For more
see The molecular structure,
classification and
naming of alkanes
Interpretation of
the infrared spectrum of heptane
The most prominent infrared absorption lines of heptane
From 2950 to 2845 cm-1 there are multiple
peaks amounting to strong absorption due to C-H stretching
vibrations in the -CH2- or -CH3 groups in
heptane.
The are other C-H absorptions due to C-H deformation
vibrations of the CH2 groups at 1480 to 1440 cm-1.
These overlap with C-H vibrations of the CH3
groups at wavenumbers 1385 to 1370 cm-1 and 1470 to 1435
cm-1.
Skeletal C-C vibrations show an absorption ~750 to
720 cm-1 for -(CH2)n-, where n is
>3, which is obviously the case with linear heptane.
There are no specific characteristic lines for
alkanes like heptane because C-C and C-H vibrations are common to so
many organic molecules and alkanes like heptane 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
heptane
molecular
structure.
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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. |
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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 image and diagram explaining the infrared spectrum
of heptane, complete infrared absorption spectrum of heptane, comparative spectra of
heptane, prominent peaks/troughs for identifying functional groups in the infrared spectrum of
heptane,
important wavenumber values in cm-1 for peaks/troughs in the infrared spectrum
of heptane, revision of infrared spectroscopy of heptane, fingerprint region analysis of
heptane, how to identify heptane from its infrared spectrum, identifying organic
compounds like heptane from their infrared spectrum,
how to analyse the absorption bands in the infrared spectrum of heptane detection of
no functional groups in the heptane molecule example of the infrared spectrum of a
molecule like heptane with a functional group
interpreting interpretation of the infrared spectrum of heptane shows presence
of no functional group Diagram of absorption of wavenumber
peaks in the infrared spectrum of heptane. Characteristic peak wavenumbers in the infrared
spectrum of heptane. Finger print identification pattern using the infrared
spectrum of heptane. Revision notes on the infrared spectrum of heptane. Matching
and deducing the structure of the heptane molecule from its infrared
spectrum. Infrared spectroscopy of aliphatic alkanes, infrared spectra of
heptane, a structural isomer of molecular formula C7H16
How do you interpret the infrared absorption spectrum of heptane How
to interpret the infrared spectrum of heptane Explanatory diagram of the
infrared spectrum of the heptane molecule in terms of its molecular
structure. Listing data of the prominent main wavenumber peaks
troughs in the infrared spectrum of heptane. How to explain the infrared
spectrum of heptane. Use of the infrared spectrum of heptane, identification
of heptane from its infrared spectrum - fingerprint wavenumber pattern
to identify the heptane molecule. The uses of the infrared spectrum of
the heptane molecule. The distinctive features of the infrared spectrum
of the heptane molecule explained interpretation diagram explaining the
peaks-trough of the transmittance of the infrared spectrum of
heptane
what does the infrared spectrum tell you about the structure and
properties of the heptane molecule? How is infrared spectrum of
heptane used
to identify heptane?
Links associated with heptane
The mass
spectrum of heptane
The H-1 NMR
spectrum of heptane
The C-13 NMR
spectrum of heptane
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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