{TAIL ~ R4} denotes hydrogen or a straight chain or branched alkyl radical which has 1 to 4 carbon atoms and is optionally interrupted in {HEAD ~ the chain} by one oxygen atom, or represents a phenyl or benzyl radical, 
{ TAIL ~ R4 } denotes hydrogen or a straight chain or branched alkyl radical which has 1 to 4 carbon atoms and is optionally interrupted in { HEAD ~ the chain } by one oxygen atom , or represents a phenyl or benzyl radical ,
TAIL TAIL TAIL TAIL TAIL 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 OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH