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