The electron donor is added directly to {HEAD ~ the mixture} of the titanium halide and {TAIL ~ the olefin} 
The electron donor is added directly to { HEAD ~ the mixture } of the titanium halide and { TAIL ~ the olefin }
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL