Analysis of Butane and Ethane

 

            The first graph is Ethane. This graph is comparing the energy of ethane with the rotation of a methyl group. The methyl group was rotated about the 1-2 carbon bond every 15 degrees. After the bond was rotated the mm2 calculated. The calculations included the torsion energy, 1,4 vdw energy and the total energy. Once the calculations were recorded the graph was plotted. On the x-axis was rotation versus the y-axis total energy.

            The second graph is Butane. This graph is comparing the energy of butane with the rotation of 2-3 carbon bond every 15 degrees. The bond energy and dihedral angles were calculated. The other calculations also included, torsion energy, 1,4 vdw energy, non-1,4 vdw energy, and the total energy. Once the calculations were recorded the graph was plotted. On the x-axis was dihedral angle versus the y-axis total energy.

            The ethane chart shows different energy conformers. The results show the maximum energies are all equal to each other. The minimum energies show there are all equal to each other. This result is due to the two carbons that are equally bonded to the three hydrogen atoms. The maximum energies occur at 60, 180 and 300 degrees. At these degrees the methyl group is eclipsed with the hydrogen atoms. The minimum energies occur at 0, 120, and 240 degrees. At these degrees the methyl group is staggered with the hydrogen atoms. When the energies are eclipsed the hydrogen energy increases. When the energies are staggered the hydrogen energy decreases because of the lack of steric interactions.

            The butane energies provided different results. The results are different because you are rotating a methyl group and two hydrogen atoms. The butane has two eclipses and one highest energy conformer. The two eclipses occur at 60 and 300 degrees where the methyl group is eclipsed with a hydrogen atom. The highest energy conformer occurs at 180 degrees where the methyl group is eclipsed with another methyl group. The two hydrogen atoms are also eclipsed with hydrogen. When these groups are eclipsed there is an increase in steric interactions which causes the high energies.

            The minimum energies are staggered and have two gauche conformations and an anti-conformation. The two gauche interactions occur at 120 and 240 degrees. The gauche interactions occur because the methyl groups are staggered from the other methyl group. The anti-conformation has the lowest energy because the two methyl groups are staggered as far away from each other as possible. The anti-conformer has slightly lower energy then the gauche interactions. The lower anti-conformer is because it has the least amount of steric interactions.  

            When comparing the ethane and butane energy each one has high and low energies when rotating around the central carbon atom. The difference is the ethane has equal maximum and minimum energies because the groups attached to the central carbon atom are equivalent. The butane energy does not have equal maximum and minimum energies because the groups attached to the central carbon atom are not equivalent to each other. The ethane has a single methyl group and the butane has two methyl groups that are rotating around the central carbon atom.

            The two different energies are show to be different due to the amount of steric interactions and the location at where these interactions occur. The Newman projections show where the all of the different interactions are occurring and the show staggered energies and eclipsed energies as the groups rotate around each other.