{HEAD ~ R2} is hydrogen, {TAIL ~ nitro}, amino or mono or dialkylamino; and 
{ HEAD ~ R2 } is hydrogen , { TAIL ~ nitro } , amino or mono or dialkylamino ; and
HEAD HEAD HEAD HEAD HEAD REL OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH