Hi Nicole,

S/R can definitely be tricky, but I usually do this to help me find a stereocenter. Look for a carbon center with at least three bonds drawn on it. Generally, they have a pretty good chance of being a stereocentre.

As for solving this problem, you will have to look for places that are similar between the reactant and the product. Looking at brevicomin, there is a two carbon chain thats stickng out from a bond to a carbon bound to an oxygen. The only time when we see something like this is on carbon #8 and 9 of the starting epoxide. So, working our way across, we will find that carbon 7 is the first in the ring, and carbon #6 is the next one that would bind to an oxygen (they labelled it carbon #1 to confuse you in the first diagram). This tells me that carbon #6 is therefore the one involved in this ring-closing mechanism.

I hope that helps, please let me know if you have any further questions!

Cheers,

Molly

Hi Nicole,

When looking at the bicyclic ring structure, the first thing that sticks out to me is the presence of a two-carbon chain on the left of the ring. Those two carbons are then attached to a carbon attached to an oxygen. The only place I see that two-carbon chain is carbon 8 and 9, which is before it hits a carbon with an oxygen attached (carbon #7) in the non-ring, open chain format of the molecule. The other location could have been carbon #1, which is connected to carbon #2 that is connected to oxygen, but that wouldn't make sense... how would I have seen a two-carbon chain sticking out from carbon #2...?

I hope that that is more clear,

Molly