wherein X is carbon or {TAIL ~ nitrogen} and can be at {HEAD ~ any position} in the ring, and 
wherein X is carbon or { TAIL ~ nitrogen } and can be at { HEAD ~ any position } in the ring , and
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH