Correlation of Solvolytic Reactivities. A New <i>Y_BnBr</i> Scale for Benzylic Bromides

Abstract

Abstract Solvolysis of 2‐bromo‐2‐(4′‐fluoromethyl)phenyladamantane (4), and 2‐bromo‐2‐(4′‐trifluoromethyl)phenylpropane (5) were carried out in a number of solvents, and their rate constants measured. Significant deviation from linear log k‐Y Br plots was observed, and the order of reactivities, e.g., k (100M) &gt; k (90E) &gt; k (80A), was in the reverse order of Swain's solvent parameter B. Different extent of solvation to the localized and the delocalized cationic transition state was then likely to play an important role. Similar result was also found in the solvolysis of 1‐bromo‐2,2,2‐trifluoro‐1‐(4′‐methylphenyl)‐1‐phenylethane (6). A new Y scale, Y BnBr, for the correlation of solvolytic reactivities of benzylic bromides based on k (4) was established. Intervention of solvent assistance in the solvolysis of 5 is discussed.