The alkaline dehydrochlorination of some naphthalene tetrachlorides and related compounds. Part II. 1,1,2,3,4-Pentachlorotetralin

Abstract

The rates and products of alkaline dehydrochlorination of 1,1,2,3,4-pentachlorotetralin and its 2- and 4-deuterio-derivatives have been examined; they establish that the primary kinetic isotope effect on both the first and second stage of the reaction is large (k_H:k_D > 7). Evidence for a small secondary deuterium isotope effect for hydrogen atoms α- to the displaced halogen (k_H:k_D= 1·12) is also obtained. Comparison with corresponding kinetic measurements on naphthalene α-tetrachloride and its octadeuterio-derivative throws light on the conformations and reaction paths involved in these reactions. The alternative paths available for dehydrochlorination, though not much affected by temperature, are substantially dependent on the solvent, in a way which indicates complex formation between certain aromatic solvents and the organic substrate, and can be correlated with solvent effects on the chemical shifts of the ¹H n.m.r. signals from the alicyclic hydrogen atoms.