The solvation, complexation; and disproportionation equilibria, which might be important during titration of a Grignard reagent RMgX with an alcohol in the presence of 1,10-phenanthroline (phen), have been studied both in the gas phase and solution using the density functional theory (DFT) B3LYP/6-31+G* method. Solvation was modeled using the supermolecule approach. NBO atomic charge analyses were performed at the B3LYP/6-31G* level. The absorption spectra of the complexes were calculated by the DFT TD/MPW1PW91/6-311+G** method. According to our calculations the complexation of magnesium halide MgX2 with 1,10-phenanthroline is the reason for the disappearance of the red color of the complex RMgX(phen) near the titration end point.