R6 and R9 are each, independently, hydrogen, {HEAD ~ alkyl} of {TAIL ~ 1 6 carbon atoms}, or aralkyl of 7 10 carbon atoms 
of
R6 and R9 are each , independently , hydrogen , { HEAD ~ alkyl } of { TAIL ~ 1 6 carbon atoms } , or aralkyl of 7 10 carbon atoms
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH