Systematic quantum chemistry calculations of electronic and geometric characteristics of four channels for interaction of a Mgn (n = 4, 10) cluster with RHal organohalides, where R = CH3, C2H5, i-C3H7, t-C4H9,C2H3, C6H5 and Hal = Cl (and partially F, Br), were performed using the DFT method (B3PW91, 6– 311+G(d)). The reaction channels are classified as radical or non-radical according to the nature of their reaction products. Regarding to Mg10...RHal, the calculated values of Gibbs free energies of activation are close to experimental values. For all the investigated cases, radical channels are preferred, but for vinyl and phenyl chlorides, this preference is only true due to the entropy factor.