|
Interpreting the infrared
spectrum of 2,3-dimethylbutane
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 2,3-dimethylbutane
email doc
brown
Use your
mobile phone or ipad etc. in 'landscape' mode
This is a BIG
website, you need to take time to explore it
Infrared spectroscopy - spectra index
See also
comparing infrared, mass, 1H NMR & 13C NMR
spectra of the structural alkane isomers of C6H14
Spectra obtained from a liquid film of 2,3-dimethylbutane. The right-hand part of the of the
infrared spectrum of 2,3-dimethylbutane, wavenumbers
~1500 to 400
cm-1 is considered the fingerprint region for the
identification of 2,3-dimethylbutane and most organic compounds. It is due to a unique set
of complex overlapping vibrations of the atoms of the molecule of
2,3-dimethylbutane.
2,3-dimethylbutane C6H14
 ,
,
For more
see The molecular structure,
classification and
naming of alkanes
Interpretation of
the infrared spectrum of 2,3-dimethylbutane
The most prominent infrared absorption lines of
2,3-dimethylbutane
For 2,3-dimethylbutane, there are strong C-H stretching vibration absorption bands at
wavenumbers 2940 to 2880 cm-1 for the CH2 and
CH3 groups.
Several strong C-H deformation vibration absorptions
at wavenumbers 1480 to 1365 cm-1 for the CH2
and CH3 groups in 2,3-dmethybutane (a double peak).
Several strong C-C skeletal vibration
absorptions associated with a C-(CH3)2
group occur at wavenumbers 1175 to 1140 cm-1 and 840
to 790 cm-1.
All of these infrared absorption vibrations are
characteristic of saturated alkyl structures in molecules,
exemplified by branched alkanes themselves e.g.
2,3-dimethylbutane.
The absence of other specific functional group bands
will show that particular functional group is absent from the
2,3-dimethylbutane
molecular
structure.
|
Comparing the infrared, mass, 1H NMR and 13C NMR
spectra of the five structural alkane isomers of C6H14
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 hexane,
2-methylpentane, 3-methylpentane, 2,2-dimethylbutane and
2,3-dimethylbutane image sizes. These five molecules
are structural isomers of saturated alkanes of molecular formula C6H14
and
exemplify the infrared, mass, 1H NMR and 13C NMR spectra of lower
aliphatic alkanes (non-cyclic alkanes). |
|
Infrared spectra below. |
 |
 |
 |
INFRARED SPECTRA:
Apart from the significant differences in the fingerprint region at
wavenumbers 1500 to 400 cm-1, there are no other
great striking differences, but each could be identified from
its infrared spectrum. All the absorption
bands are typical of molecules containing saturated alkyl structure and
there are no characteristic infrared absorptions due to a specific
functional group. |
 |
|
|
Infrared spectra above, mass spectra below. |
 |
 |
 |
MASS SPECTRA: Base ion
peaks plus m/z comments.
Hexane: m/z 57, 42 and 56 prominent
2-methylpentane: m/z 43, 42 and 71 prominent
3-methylpentane: m/z 57, 41 and 56 prominent
2,2-dimethylbutane: m/z 43, 41, 57 and 71
prominent
2,3-dimethylbutane: m/z 43, 41, 42 and 71
prominent |
 |
 |
|
Mass spectra above, 1H NMR spectra below. |
 |
 |
 |
1H NMR SPECTRA: They can
all be distinguished by their different integrated proton ratios -
need very high resolution.
Hexane:
3 1H
δ shifts, H ratio 3:2:2 (6:4:4 in formula)
2-methylpentane:
5 1H
δ shifts, H ratio 6:3:2:2:1
3-methylpentane:
4 1H
δ shifts, H ratio 6:4:3:1
2,2-dimethylbutane: 3 1H
δ shifts, H ratio 9:3:2
2,3-dimethylbutane: 2 1H
δ shifts, H ratio 6:1 (12:2 in formula) |
 |
 |
|
1H NMR spectra above, 13C NMR spectra below. |
 |
 |
 |
13C NMR SPECTRA: From the
number of shifts, you can't distinguish (iii) and (iv) but you can
distinguish them from (i), (ii) and (v). (i) Hexane: 3 13C
δ shifts
(ii) 2-methylpentane: 5 13C
δ shifts
(iii) 3-methylpentane: 4 13C
δ shifts
(iv) 2,2-dimethylbutane: 4 13C
δ shifts
(v) 2,3-dimethylbutane: 2 13C
δ shifts |
 |
 |
|
13C NMR spectra above. |
Key words & phrases: image and diagram explaining the infrared spectrum
of 2,3-dimethylbutane, complete infrared absorption spectrum of
2,3-dimethylbutane, comparative spectra of
2,3-dimethylbutane, prominent peaks/troughs for identifying functional groups in the infrared spectrum of
2,3-dimethylbutane,
important wavenumber values in cm-1 for peaks/troughs in the infrared spectrum
of 2,3-dimethylbutane, revision of infrared spectroscopy of 2,3-dimethylbutane, fingerprint region analysis of
2,3-dimethylbutane, how to identify 2,3-dimethylbutane from its infrared spectrum, identifying organic
compounds like 2,3-dimethylbutane from their infrared spectrum,
how to analyse the absorption bands in the infrared spectrum of
2,3-dimethylbutane detection of functional groups in the 2,3-dimethylbutane molecule example of the infrared spectrum of a
molecule like 2,3-dimethylbutane with a functional group
interpreting interpretation of the infrared spectrum of 2,3-dimethylbutane
Diagram of absorption of wavenumber
peaks in the infrared spectrum of 2,3-dimethylbutane. Characteristic peak wavenumbers in the infrared
spectrum of 2,3-dimethylbutane. Finger print identification pattern using the infrared
spectrum of 2,3-dimethylbutane. Revision notes on the infrared spectrum of
2,3-dimethylbutane. Matching
and deducing the structure of the 2,3-dimethylbutane molecule from its infrared
spectrum. Infrared spectroscopy of aliphatic
alkanes, infrared spectra of
2,3-dimethylbutane, a structural isomer of molecular formula C6H14
Links associated with 2,3-dimethylbutane
The chemistry of ALKANES
revision notes INDEX
The mass spectrum of
2,3-dimethylbutane
The H-1 NMR spectrum of
2,3-dimethylbutane
The C-13 NMR spectrum of
2,3-dimethylbutane
Infrared spectroscopy index
ALL SPECTROSCOPY INDEXES
All Advanced Organic
Chemistry Notes
Use My Google search site box
Email doc b:
chem55555@hotmail.com
|
