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