Influence of Substituents on Reactivity and Reaction Mechanism of SN Reaction of Some Organophosphorus Compounds; Relied on Linear Free Energy Relationship

The tetracoordinated organophosphorous compound (4 - Chlorophenyl 4 - methyl phenyl Chlorophosphate, 1) were synthesized, characterized and nucleophilic substitution reaction (pyridinolysis) were investigated in acetonitrile at 5.0oC by varying substituents in nucleophiles. The reactivity is expressed in terms of second-order rate constant, k2 and measured conductometrically. Physical organic chemistry tools mainly Hammett (ρ), Brönsted (β) Linear Free Energy Relationship (LFER) coefficients being determined in quest for the mechanistic information by comparing pyridinolysis of structurally similar organophosphorous compounds reported earlier. Nice linear correlation being found for Hammett (logk2 vs σx) and Brönsted (logk2 vs pKa(x)) plots. In the light of the reported results the LFER obtained for 1 with negative value of the ρX, −5.78 and large positive value for βX, 1.17 can be interpreted as SN2 process, with greater extent of bond formation in TS of 1.