Equilibrium acidities in dimethyl sulfoxide solution have been found to increase along the series Me, Et, i-Pr, t-Bu for 9-substituted fluorenes when the alkyl group, R, is separated from the fluorene ring by a CHz, S, or SO2 moiety. This is a reversal of the effect observed when R is attached directly to the fluorene ring. Separation of the t-Bu group from the fluorene ring by a second CH2 moiety causes the acidifying effect to disappear. A stabilizing, through- ...