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