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