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