A compound of the formula: ##STR38## wherein R1 and R2 are selected from the group consisting of hydrogen, methyl and ethyl, wherein R1 and {HEAD ~ R2} cannot both be {TAIL ~ hydrogen} simultaneously 
not be
A compound of the formula : # # STR38 # # wherein R1 and R2 are selected from the group consisting of hydrogen , methyl and ethyl , wherein R1 and { HEAD ~ R2 } can not both be { TAIL ~ hydrogen } simultaneously
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH REL OTH REL TAIL TAIL TAIL TAIL TAIL OTH