How can you determine E and Z isomers in a molecule?

1 Answer
Mar 23, 2018

Priority is assigned to substituents about the double bond (remember absolute configuration?). When both of the highest priority groups are on the same side, it is #Z#, when they are on opposite sides, it is #E#.

For instance, consider pladienolide B,

puu.sh #""^1#

I highlighted the bond in consideration so you wouldn't be playing Where's Waldo?!

The ring system to the right would be considered highest priority per the normal rules, and the #"sp"^2# carbon to the left it is connected to would be considered highest priority.

They are on different sides. Hence, this is an #E# geometric isomer of pladienolide B.

For fun, it has approximately 256 stereoisomers it could be, and here is its enantiomer,

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where all of its chirality centers (not the one on the #"sp"^2# carbon because it has three connections, not four!) are inverted.

#""^1# Org. Lett. 2012, 14, 4730-4733