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