SOLVENT EFFECTS ON THE SOLVOLYSIS OF 2-ARYL-1,1-DIMETHYLETHYL BROMIDES

Solvolysis rates of substituted 2-aryl-1,1-dimethylethyl bromides (1) were determined in a variety of solvents such as aqueous mixtures of e thanol, acetone; 2,2,2-trifluoroethanol, and also mixtures of ethanol and TFE at 25 degrees C, 35 degrees C, and 45 degrees C. The solvent e ffects were analyzed in terms of Winstein-Grunwald equation. The solve nt effects of 1-4-MeO failed to give a single linear correlation again st either Y or Y-Cl (Y-Br), but exhibited a wide split pattern which c ould not be related to the solvent nucleophilicity. On the other hand 1-4-CH, and 1-H gave a fairly good linearity. In the case of 1-4-MeO, a fairly good linearity was observed against Y, defined from the solvo lysis of 4-methoxyneophyl tosylate. It is assumed that resonance inter action between reaction site and aryl-pi-system operates to give charg e delocalization regardless of the different solvolysis mechanisms. Th e Hammett-Brown treatment of the solvolytic rate constant of compounds 1 was obtained non-linear two separated lines of -1.06 to -1.46, sugg esting of mechanistic changeover from k(c)-k(s) to k(Delta) on going f rom electron-withdrawing to electron-donating substituents as a basis of 4-CH3 group.