{HEAD ~ R4} is halogen, {TAIL ~ alkoxy}, phenylthio or phenoxy, which may be substituted or unsubstituted 
is
{ HEAD ~ R4 } is halogen , { TAIL ~ alkoxy } , phenylthio or phenoxy , which may be substituted or unsubstituted
HEAD HEAD HEAD HEAD HEAD REL OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH