Problem Set 2 Question

[Michelle_Nguyen_3F]

Hello! I understand that when determining whether a molecule is cis or trans, we give the higher priority to the atom with the larger atomic molecule. In this case, I know Br has the higher priority, but how do we know that it is trans since on the other side, they are both CH3 and thus have the same priority. Also, do we need to do the trans/cis classification for both double bonds? Thank you!

[Chem_Mod]

Hello! I understand that when determining whether a molecule is cis or trans, we give the higher priority to the atom with the larger atomic molecule. In this case, I know Br has the higher priority, but how do we know that it is trans since on the other side, they are both CH3 and thus have the same priority. Also, do we need to do the trans/cis classification for both double bonds? Thank you!

This is absolutely not how cis/trans works. You are describing E/Z classification system. Do NOT mistake them as they are completely different. Cis/trans uses the longest carbon chain. E/Z uses higher atomic numbers. If you are having trouble understanding how to use both, just use one (I prefer E/Z as it is very straightforward).