L1 is ##STR24## where R5 and {HEAD ~ R6} are independently a hydrogen, alkyl or {TAIL ~ an aryl group} 
are independently
L1 is # # STR24 # # where R5 and { HEAD ~ R6 } are independently a hydrogen , alkyl or { TAIL ~ an aryl group }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL REL OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL