{HEAD ~ Another order} of addition involves initially contacting {TAIL ~ the electron donor} with the co catalyst 
involves initially contacting
{ HEAD ~ Another order } of addition involves initially contacting { TAIL ~ the electron donor } with the co catalyst
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH