{HEAD ~ R} is {TAIL ~ a lower, straight chain alkyl group} having 1 to 4 carbon atoms 
is
{ HEAD ~ R } is { TAIL ~ a lower , straight chain alkyl group } having 1 to 4 carbon atoms
HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH