Solvent and substituent effects in the solvolysis of 9-aryl-9-bromofluorenes

The solvolysis of eight 9-aryl-9-bromofluorenes (6b similar to 6i) in a var iety of solvents were studied. Correlation analysis using single-parameter Grunwald-Winstein equation (Eqn. 1) with different Y scales showed good lin earity (R greater than or equal to 0.98) for most cases if Y-xBnBr was empl oyed. Linear relationships were observed from Hammett-type analysis of loga rithm of rate constants using Brown-Okamoto sigma(+) constants (Eqn. 3), al though inverse order of k(p-CF3)/k(m-CF3) was realized in a number of cases . The rho values were found to vary slightly with different solvent systems . Calculated atomic charge reveals the similarity between 9-phenyl-9-fluore nyl cation (7) and triphenylmethyl cation (8). An extended charge delocaliz ation throughout the fluorenyl ring led to the conclusion of the insignific ance of antiaromaticity, which was in harmony with that obtained in previou s studies. The variation of relative k(Br)/k(Cl) rate ratios was attributed to the electrophilic pull by solvents in solvolysis.