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