Numbering heteroatoms and groups in benzene derivatives Can someone please explain why the carbon in 8-hydroxyquinoline is numbered 8, while in 1,10-phenanthroline the nitrogens are numbered 1 and 10? I'm counting carbon atoms and just cannot see why the hydroxy is in position 8 and nitrogen atoms are in positions 1 and 10.
Quaternary carbon atoms i.e. Those with no hydrogen atoms attached and in these examples, the ones that are common to both or all rings, are not counted. Try it with 1,8-dihydroxynaphthalene. Both OH groups should be pointing in the same direction.

In your examples, as you probably know, the heteroatom is numbered first.