Defining your structures

To be able to actually use the structures as described earlier, it is necessary to define one of the atoms as having xyz-coordinates (0,0,0). This will then be the atom that will actually appear at the spot of the atom that is replaced by the structure.

Place a 'Methyl' structure in the drawing area
Replace the hydrogen atoms by chloride atoms and pre-optimize
Select the central carbon atom
Choose Edit → Set Origin
Save the structure in (a subdirectory of) your $SCM_STRUCTURES directory

The new structure will in the structures menu and can be directly used.