Winter 2012 Final Q5

[Annabel Hou 1C]

Why does the molecule cyclooct-4-enone have a cis- geometry?

[Irena Roy 4H]

Look at the carbons connected to the double bond. Now look at the atoms connected to those carbons. On the left side of the double bond, a C and an H are connected to the carbon you just located. C has a higher atomic number than H, so mark C. Now look at the right side of the double bond. Another C and H are connected to the other carbon you located. Since C has a higher priority, mark that one. Now look at the two carbons you marked. Both are on the same side of the double bond (above it), giving it a -cis geometry.

[Amy Pai]

I thought you move on if there's a tie with priority (so keep going through the carbons until you hit something different)? And where are the different functional groups what we need to mark for priority? Like from the left side it's the ketone (O as priority), but from the right its just carbons until it connects with the ketone...