Linear free energy relationships in the thiophene series. Part 3. A kinetic study of chlorine-isotopic exchange between lithium chloride and some 2-chloro-3-nitro-5-X-thiophenes

Abstract

The rate constants for the chlorine-isotopic exchange between lithium chloride-36 and some 2-chloro-3-nitro-5-X-thiophenes (la—g) have been measured in sulpholane solution. The results obtained give a good Hammett correlation (in the range 323–373 K; calculated ρ 5.55—4.68), indicating that the charge developed in the transition state is strongly affected by the electronic effects of substituents. In order to study the effect of solvent on reactivity, the rates of 2-chloro-3,5-dinitrothiophene (lg) have also been measured in acetone, methanol, and propan-2-ol solutions. A comparison has been made between thiophene and benzene derivatives and the MNDO technique has been used to provide a theoretical model of the exchange reaction.