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Interpreting the infrared
spectrum of 3-methylhexane
Doc
Brown's Chemistry Advanced Level Pre-University Chemistry Revision Study
Notes for UK IB KS5 A/AS GCE advanced A level organic chemistry students US
K12 grade 11 grade 12 organic chemistry courses involving molecular
spectroscopy analysing infrared spectra of 3-methylhexane
See also
comparing the
1H NMR and 13C NMR spectra of the nine alkane structural isomers of C7H16
Spectra obtained from a liquid film of 3-methylhexane. The right-hand part of the of the
infrared spectrum of 3-methylhexane, wavenumbers
~1500 to 400
cm-1 is considered the fingerprint region for the
identification of 3-methylhexane and most organic compounds. It is due to a unique set
of complex overlapping vibrations of the atoms of the molecule of
3-methylhexane.
3-methylhexane C7H16
Interpretation of
the infrared spectrum of 3-methylhexane
The most prominent infrared absorption lines of
3-methylhexane
From 2975 to 2845 cm-1 there are multiple
peaks amounting to strong absorption due to C-H stretching
vibrations in the -CH-, -CH2- or -CH3 groups in
3-methylhexane.
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.
There are weak C-H vibrations of the -CH- group at
~1340 cm-1, close to the C-H vibrations of the -CH3
groups.
There are strong C-C skeletal vibration absorptions
at 1175 to 1140 cm-1 from the C(CH3)2
grouping, and similarly, but, weaker, an absorption at 840 to 790 cm-1.
There are no specific characteristic lines for
alkanes like 3-methylhexane because C-C and C-H vibrations are common to so
many organic molecules and alkanes like 3-methylhexane 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
3-methylhexane
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 |
|
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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 |
 |
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3 δ: proton ratio:
12:2:2 |
3 δ
shifts |
| 3,3-dimethylpentane |
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3 δ: proton ratio:
3:3:2 (6:4:4 in the molecule) |
4 δ
shifts |
| 2,2,3-trimethylbutane |
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3 δ: proton ratio:
9:6:1 |
4 δ shifts |
Key words & phrases: C7H16 image and diagram explaining the infrared spectrum
of 3-methylhexane, complete infrared absorption spectrum of 3-methylhexane, comparative spectra of
3-methylhexane, prominent peaks/troughs for identifying functional groups in the infrared spectrum of
3-methylhexane,
important wavenumber values in cm-1 for peaks/troughs in the infrared spectrum
of 3-methylhexane, revision of infrared spectroscopy of 3-methylhexane, fingerprint region analysis of
3-methylhexane, how to identify 3-methylhexane from its infrared spectrum, identifying organic
compounds like 3-methylhexane from their infrared spectrum,
how to analyse the absorption bands in the infrared spectrum of 3-methylhexane detection of
no functional groups in the 3-methylhexane molecule example of the infrared spectrum of a
molecule like 3-methylhexane with a functional group
interpreting interpretation of the infrared spectrum of 3-methylhexane shows presence
of no functional group
CH3CH2CH(CH3)CH2CH2CH3
Diagram of absorption of wavenumber
peaks in the infrared spectrum of 3-methylhexane. Characteristic peak wavenumbers in the infrared
spectrum of 3-methylhexane. Finger print identification pattern using the infrared
spectrum of 3-methylhexane. Revision notes on the infrared spectrum of
3-methylhexane. Matching
and deducing the structure of the 3-methylhexane molecule from its infrared
spectrum. Infrared spectroscopy of aliphatic alkanes, infrared spectra of
3-methylhexane, a structural isomer of molecular formula C7H16
Links associated with 3-methylhexane
The chemistry of ALKANES
revision notes INDEX
Infrared spectroscopy index
ALL SPECTROSCOPY INDEXES
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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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