The coupling reagent couples with {HEAD ~ this diazo compound} to produce {TAIL ~ an azo dye} 
to produce
The coupling reagent couples with { HEAD ~ this diazo compound } to produce { TAIL ~ an azo dye }
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL