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