{HEAD ~ X} is selected from the group consisting of O , S , and >N R5, wherein R5 is hydrogen or {TAIL ~ an alkyl group} having from 1 to 9 carbon atoms 
{ HEAD ~ X } is selected from the group consisting of O , S , and > N R5 , wherein R5 is hydrogen or { TAIL ~ an alkyl group } having from 1 to 9 carbon atoms
HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH