Large patch (80kB), removing a lot of use of Molecule, Ring, and DefaultChemObjectBuilder.
I have uploaded a new, rebased version of the patch, against today's master.
The patch is also available from my GitHub page:
The patch looks OK. It's a bit weird that ReactionChain is in "extra" package and not in the reaction package, but this is to avoid a direct dependency on the data package.
Pushed to master.