Solvent and Substituent Effects in the Solvolysis of 9‐Aryl‐9‐bromofluorenes

The solvolysis of eight 9‐aryl‐9‐bromofluorenes ( 6b∼6i ) in a variety of solvents were studied. Correlation analysis using single‐parameter Grunwald‐Winstein equation (Eqn. 1) with different Y scales showed good linearity ( R ≥ 0.98) for most cases if Y xBnBr was employed. Linear relationships were observed from Hammett‐type analysis of logarithm of rate constants using Brown‐Okamoto σ + constants (Eqn. 3), although inverse order of k ( p ‐CF 3 )/ k ( m ‐ CF 3 ) was realized in a number of cases. The ρ values were found to vary slightly with different solvent systems. Calculated atomic charge reveals the similarity between 9‐phenyl‐9‐fluorenyl cation ( 7 ) and triphenylmethyl cation ( 8 ). An extended charge delocalization throughout the fluorenyl ring led to the conclusion of the insignificance of antiaromaticity, which was in harmony with that obtained in previous studies. The variation of relative k Br / k Cl rate ratios was attributed to the electrophilic pull by solvents in solvolysis.