Traditional formulations of Ziegler-Natta catalysts that are based on magnesium ethoxide tend to generate titanium moieties presenting ethoxide ligand. It is suggested that the ethoxide group in the coordination sphere of titanium affects the catalyst activity and molecular weight distribution of the produced polymer. In the present work, a systematic synthesis of catalyst and chemical characterizations were accomplished with the objective of identifying correlations between the active sites presenting ethoxide as ligand and the performance of the catalyst in terms of activity and average molecular weight. Octahedral and trigonal-bipyramidal titanium moieties were identified as two groups of active sites in the catalyst. The ethoxide group as a ligand of the titanium was found in octahedral moieties only. Trigonal-bipyramidal titanium moieties have preferentially chlorine as ligands.