 |
| Introduction |
| Symmetry Elements |
| · Proper Rotation Axis |
| · Mirror Plane |
| · Inversion Centre |
| · Improper Rotation Axis |
| · Identity |
| Point Group Gallery |
| Spotting a Chiral Compound |
| · Part I - Mirror Planes |
| · Part II - Inversion Centre |
| · Part III - Improper Rotation |
| · Summary & Conclusion |
| WSM Homepage |
Molecular Symmetry and Chirality
Improper Rotation Axis
Note: viewing the structures on these pages requires use of
the MDL Chime Plug-In.
The Sn operation rotates a molecule about an axis by 360º/n, and then reflects through a mirror plane orthogonal to that axis. In effect, the Sn operation equals the sequential operations Cn + σh, although the presence of an Sn element does not always imply the presence of either a Cn or σh element alone.
An Sn element with an odd n value requires both Cn and σh elements. An Sn element with an even n value may or may not have these elements.
The S1 operation is identical to σ, while the S2 operation is identical to i.
|
Re(CH3)6 has an S3 improper rotation axis. Note that the odd value of n means that the compound also has a C3 axis and a σh mirror plane.
|
|
Methane has a four S4 improper rotation axes. Note that the value of n is even, and that in this case there is neither a C4 axis nor a σh.
|
This page is maintained and copyright by W. Stephen McNeil at UBC Okanagan.
.