{HEAD ~ R7} represents H, C1 4 alkyl or {TAIL ~ trifluoromethyl} 
represents
{ HEAD ~ R7 } represents H , C1 4 alkyl or { TAIL ~ trifluoromethyl }
HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL