Comparison of the Numbers and Kinds of Symmetry Elements in Eclipsed and Staggered Ethane
Holding a model of ethane (or two) in your hand would really help you here.
Click on the symmetry element to go to explainations. |
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Eclipsed Ethane (CH3CH3, with H - lined up) & Staggered Ethane (CH3CH3, with H - not lined up) |
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The principal rotation axis has the highest "order" -- C3 > C2 in this case. There is only one C3 in ethane. |
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Inversion Center -- located at center of molecule (0, 0, 0)
each atom at x, y, z is inverted through the center to -x, -y, -z. |
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If there is one C2 axis perpendicular to the principal axis (Cn), then there will be n C2 axes.
Locate all of them. |
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A horizontal mirror is defined as being perpendicular to the principal axis.
It is also called a "sigma-h" written as sh. |
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Vertical mirrors contain the principal axis.
Dihedral mirrors are located between two rotation axes or two vertical mirrors. |
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Any species with a horizontal mirror will have an Sn collinear with the Cn.
Some species have an S2n collinear with a Cn when there is no horizontal mirror. |
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Every species has one and only one identity. |
The conformations of ethane have only horizontal, vertical and dihedral mirrors. |
A C3 axis has no other axis collinear with it. |
