{HEAD ~ Y} is {TAIL ~ a halide, sulfate, phosphate, or p toluenesulfonate anion} 
{ HEAD ~ Y } is { TAIL ~ a halide , sulfate , phosphate , or p toluenesulfonate anion }
HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL