C2H2F2Cl2 C2H2F2Cl2 C2H2F2Cl2
View perpendicular to C-C axis Oblique view View down C-C axis

This molecule has a particular symmetry in this conformation (assuming idealised tetrahedral geometry for the bonds around the carbon atoms): the only symmetry element present is the point of inversion in the middle of the C-C bond. You should note that although each carbon atom is chiral the molecule as a whole is not: molecules with a point of inversion are never chiral. Compare the symmetry of this molecule to that of the chiral R,R′ CHFBr-CHFBr molecule.

The point-group symmetry for this molecule is given the crystallographic symbol -1.

Applying a torsional twist about the C-C bond of 180° to this molecule results in a conformation with a different point-group symmetry. What symmetry element is present in this new conformation?

© Copyright 1997-2006.  Birkbeck College, University of London. Author(s): Jeremy Karl Cockcroft