Originally Posted by kiwi33

"over my head
bobby"

This is not easy to explain.

In a benzene ring (a hexagon of six carbon atoms) the electrons between the carbon atoms are not in fixed positions; rather they are "smeared out" across the ring. This is what is indicated in the link that mrsD provided (a hexagon with a circle in the middle of it).

In the links which Mari provided for the structures of Sinequan and Silenor there are different patterns of electrons in the two benzene rings. This is confusing - it would have been clearer to use the hexagon/circle image as in mrsD's link.

The bottom line, as mrsD has emphasised, is that Sinequan and Silenor are chemically identical (they are both doxepin) and so will have identical pharmacological properties.