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Experiment B:
Rotation of C-C Bonds
Briana HalbertFebruary 12, 2013
301-60Dr. Nwokogu
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Purpose/Background: The purpose of this experiment was to use the web
software
http://www.wetche.cmbi.ru.nl//organic//to stimulate the rotations of C-C bonds and view
the energy emitted from the different angles of rotation. Hydrocarbon atoms with two or
more carbons experience different energy levels when a bond is rotated. The positions of
the hydrogens or hydrocarbon groups attached to the specified C-C bond affect the
amount of energy produced by the molecule. Positions such as eclipse and staggered
(including gauche staggered and anti staggered) give off significantly higher and lower
energy.
We represent these rotations as Newman Projections. Here is an example of a
butane Newman Projection1:
A Newman Projection as defined by professor Harding of UCLA as a way to
analyze noncyclical conformations. Conformations being the different shapes the
molecule can bend into.2 Tension is created between the different charges of the atoms of
the atoms as they rotate around the bond and that is what is focused on in this experiment.
Carbon-carbon bonds single bonds allow the free rotation on the carbons axis. The
structure of butane has two different structures, gauche (torosional angle between methyl
groups being 60) and anti (torosional angle between methyl groups being 120).
Between the two conformations, the anti conformation group is more stable than the
gauche conformation group because of the distance between the two methyl groups in the
arrangement of the structures.
http://www.wetche.cmbi.ru.nl/organic/http://www.wetche.cmbi.ru.nl/organic/http://www.wetche.cmbi.ru.nl/organic/7/27/2019 C CBondRotation
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Table of Reagents: There were not any reagents in this experiment but the structures of the
molecules are as followed.
Butane 2-Methylbutane 2,3-Dimethylbutane
Procedure/Observations: The experiment was conducted on a computer. The site
http://wetche.cmbi.ru.nl/organic/ was Googled and accessed. Using the molecule editor sight,
ethane was modified to represent butane. In the input box, two lines were labeled. One read C2-
C3 Rotation of butane and other was made to read CHE301. After this was applied and the
rotation was calculated, the energy numbers at 10 degree variations was recorded. A butane
molecule was created and it was confirmed that it was eclipsed. Both of the carbons of the
molecules that were pointing up were replaced with methyl 1 groups and the input file lines of
the data were changed. All of the changes were applied and data was given for the inputs. All of
the data was copied and recorded in Table 1. All of the data was collected and recorded from thedata tables received from Mol4d.
Table 1:
Degrees Butane (KJ/mol) 2-Methylbutane
(KJ/mol)
2,3-Dimethylbutane
(KJ/mol)
0 13.796 11.883 17.804
10 13.032 11.423 16.496
20 11.290 9.885 13.107
30 8.939 7.244 8.594
40 6.689 5.077 4.745
50 4.838 4.104 2.824
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60 4.088 3.554 1.462
70 3.183 3.745 .490
80 3.321 4.417 .200
90 3.891 6.203 1.560
100 5.143 8.743 4.157
110 6.225 10.823 6.510
120 6.657 11.864 7.770
130 5.903 11.381 6.799
140 4.653 9.583 4.621
150 3.026 7.122 2.214
160 1.554 4.388 .670
170 .426 2.057 .138
180 .000 .710 .008
190 .429 .077 .138
200 1.620 .049 .817
210 3.139 .690 2.334
220 4.706 2.045 4.763
230 5.892 3.330 6.697
240 6.406 3.931 7.462
250 6.116 3.580 6.508
260 5.138 2.441 4.069
270 3.902 1.040 1.499
280 3.107 .666 .309
290 3.062 .000 .476
300 3.668 .526 1.604
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310 4.846 1.593 2.276
320 6.676 3.712 4.546
330 8.968 6.104 8.529
340 11.317 8.969 12.879
350 14.097 10.828 16.176
360 13.820 11.963 17.646
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Discussion:
In the Newman projections, the proximal and distal parts of the compound are visual and
aids in seeing how the rotation of the molecule works, or the torosional angle works. The energy
of the molecules depend on the strain being put on it. There are a variety of conformational
strains spanning from eclipse, partially eclipse, gauche, and anti. The different strains all
depend on the rotational state of the single bond, which is called the torosional strain. It reaches
its maximum at the eclipsed conformation. The eclipse strain contains a torosional and steric
strain whereas the partially eclipsed strain only contains the torsional strain. The gauche strainonly contains the steric strain and the anti strain contains no strain at all.
The significance of this experiment was becoming aware of how different orientations of
a molecule of conformations can produce different energies. The limitations of the experiment
however extend to the experiment however extend to the equipment used. There can be
faultiness in the software and computer programs. What would have helped more in grasping the
rotation concept would have been a hands-on ball stick model structure. What was learned is that
when groups are eclipsed in a molecule they are unstable and have high tension and energy.
With the data received from the Mol4D models, it is seen that from the rotation of butane
the methyl groups form an eclipsed conformation but at the angles of 80 and 290, the molecule
reaches a gauche conformation. At the angles of 120 and 240, the molecule reaches the partially
eclipsed conformation and at angle 180 it reaches the lowest energy level at the anti
conformation.
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Butane
2-Methylbutane
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2,3-Dimethylbutane
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