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