Structure and Reactivity of Alkylchloroformates. MO Theoretical Interpretations on Halide Exchange Reaction

[摘要] CNDO/2 MO theoretical studies and kinetic studies of halide exchange reactions for alkylchloroformates have been carried out in order to investigate structure-reactivity relationship of alkylchloroformates. From the result of energetics, it was concluded that the most stable configuration of alkylchloroformate is that in which alkyl group and chlorine are trans to each other, and that the hindered rotation about the bond between the carbonyl carbon and alkoxy-oxygen bond is attributed to the ¥ð-electron delocalization. It has been found that the large charge separation is due to -M effect of carbonyl and alkoxy oxygens and-I effect of chlorine. The order of rates in solvents studied was (CH3)2 > CO > CH3CN ¡í MeOH. The nucleophilic order showed the qualitative trends of I- > Br- > Cl- in protic solvent, and of Cl- > Br- > I- in dipolar aprotic solvents. Alkyl group contribution has the decreasing order of CH3-> C2H- ¡í i-C3H7-. The solvent effect has been interpreted on the basis of initial and final state contribution. A transition state model has been suggested, and it has been proposed that the most favorable mechanism is the addition-elimination. From the results of activation parameters and electronic properties, an energy profile has been proposed. Structural factors determining reactivities of alkylchloroformates have been shown to be charge, energy level of ¥ò* LUMO to C-Cl bond and ¥ò* antibonding strength with respect to C-Cl bond in this MO. Charge and polarizability of nucleophile, and the interaction of these effects with solvent structures are also found to be important.

[学科分类] 化学（综合）