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