C CBondRotation

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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/


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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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C CBondRotation