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