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