{HEAD ~ R25} is hydrogen, alkyl of {TAIL ~ 1 6 carbon atoms}, or aralkyl of 7 10 carbon atoms 
{ HEAD ~ R25 } is hydrogen , alkyl of { TAIL ~ 1 6 carbon atoms } , or aralkyl of 7 10 carbon atoms
HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH