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