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