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