Solvolysis of 2-aryl-2-chloroadamantanes. A new Y scale for benzylic chlorides
作者:Kwang Ting Liu、Hun Chang Sheu
DOI:10.1021/jo00009a018
日期:1991.4
A series of 2-aryl-2-chloroadamantanes 2, Ar = 4'-methylphenyl, 4'-fluorophenyl, phenyl, 3'-chlorophenyl, 3'-(trifluoromethyl)phenyl, and 4'-(trifluoromethyl)phenyl, were prepared, and the solvolytic rate constants in 23 solvents were measured. Significant deviation from linear log k - Y(Cl) plots (m = 1.002, R = 0.959) was observed, and some orders of reactivities, e.g., k(100M) > k(90E) > k(80A), were in the reverse order of Swain's solvent parameter B. Different extent of solvation to the cationic transition state was then likely to play an important role. Excellent linear correlations between the logarithms of the ks for any pair in 2a-2f were realized, and the best one was that with respect to 2d. A new Y scale, Y(BnCl), for the correlation of solvolytic reactivities of benzylic chlorides based on k(2d) was established accordingly. The observation of decreasing m values with increasing electron-attracting ability of the substituent on the aryl ring of 2 also suggested the importance of charge delocalizations.