What drives a ring-closing metathesis forward?

• Extra catalyst added at the end
• The small alkene fragment escaping as a gas
• Heating until the solvent boils away

What is a metallacyclobutane?

• A four-membered ring of metal and carbon that swaps alkene ends
• A cage of solvent around the catalyst
• The small fragment that escapes as a gas

Metathesis trades the ends of two alkenes, so each product mixes halves.

The same diene is run very concentrated. What happens?

• Only small rings form, and faster
• Nothing about the outcome changes
• Molecules join neighbours into chains

A diene chain of 8 atoms closes and a 2-carbon fragment leaves. How many atoms are in the ring?

Why does the escaping fragment move the mixture forward?

• Escaped product cannot react back, so the ring accumulates
• The gas stirs the mixture for free
• The gas feeds fresh catalyst into the flask

A student draws the products keeping each alkene's original partner. What is wrong?

• Nothing is wrong: partners never change
• The drawing is fine but drawn too slowly
• The ends trade partners, so products must mix halves

You must close a large ring whose ends can both be alkenes. Which cut fits metathesis?

• A cut that leaves matching polar handles for a carbonyl route
• A cut that leaves an alkene on each side to stitch shut
• A cut through the longest plain single-bond chain