Cis or Trans Isomer: John's Question Answered

[jaumzaum]

The compound below is cis or trans?

I learned that when the same ligants are at the same side of the bond, the isomerer is -cis, and when they are across, it is -trans. So I would say it is a cis compound

Wikipedia, though, sai it is trans. They consider the backbone chain ligants. If the backbonechain ligants are at the same side it's cis, otherside, trans.

So everything I learned was fake? I've seen nowhere else to treat cis/trans isomerer considering the backbone chain. What's the real answer?

Thanks
John

 

[Borek]

cis-trans works for simple molecules, when it is obvious with substituents are the important ones - say but-2-ene - two methyls and two hydrogens, so it is obvious that we mean methyls to be cis or trans. In the case of a molecule like the one you posted it becomes more difficult, as it is not necessarily clear which two substituents are the important ones. Here it is better to use E/Z notation, as it is unambiguous.