{HEAD ~ R16} and R17 are each, independently, hydrogen, alkyl of {TAIL ~ 1 12 carbon atoms}, or n Ar 
{ HEAD ~ R16 } and R17 are each , independently , hydrogen , alkyl of { TAIL ~ 1 12 carbon atoms } , or n Ar
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