final 2012 Q6D: (Z) or (E) forms of a pentene

[Phuong Pham 3G]

The question asks for the line structure of (Z)-3-bromopent-2-ene but how do you draw a (E)-3-bromopent-2-ene?

[Chem_Mod]

The groups attached to the double bond are:
-Bromine, ethyl (Br is heavier than C so Br takes priority)
-Methyl, H (C is heavier than H so methyl takes priority)

So we compare the locations of Methyl and Bromine. In (E) they are across, in (Z) they are the same side.

[Neil DSilva 1L]

Here's a picture showing you both the E/Z forms of the molecule. I just took the molecule from the answer in the practice final and rotated it on its side to focus on the double bond. The stars indicate the priority molecule on either side of the double bond.

[Chem_Mod]

Thanks for uploading it Neil!