These are molecules that have a flat area (phenyl), with a bridge that joins their ends either on the top or bottom face.

1. We assign names to certain atoms as shown in the image. "z" is the first atom that is out of plane. Two chains start from x, to which we must give priority by atomic number.

2. We project the xy link, placing ourselves in the position of the arrow.

3. Finally we turn from "a" to "z". If the rotation is clockwise the plane is Rp, if it is in the opposite direction Sp.

If the chain goes at the bottom we have the enantiomer. Therefore, long chains that can pass from top to bottom generate optically inactive racemates.