Steering the next group

Each group on a benzene ring directs the next substituent to the meta position or to the ortho and para positions. You will put a table of directors to work.

The idea. If every position were equally likely, a ring with one group would give 2 ortho, 2 meta and 1 para product. A real group changes these shares.

Your tasks.

1. Set place_nitro to the directing class of the nitro group, "meta" or "ortho-para".
2. Set meta_directors to the sorted list of the groups that direct meta.
3. Set percent_para to the percentage of para product if all positions were equally likely.
4. Set para_over_ortho to the ratio of the para share to the ortho share of toluene, from the data.