Effect of oxime substituents on 9-fluorenyl carbocations

9-Fluorenyl carbocations substituted with the oxime functional groups CH=NO CH3, CH3C=NOCH3, and i-PrC=NOCH3 were generated by solvolyses of the corres ponding chlorides in methanol, These cations form at rates which greatly ex ceed those of formation of the parent 9-fluorenyl cation. Relative rate dat a suggest that stabilization of 9-fluorenyl cations by CH=NOCH3 is greater than stabilization by CH3C=NOCH3, which is in turn greater than that by i-P rC=NOCH3. Computational studies on these cations show that the oxime group is progressively rotated out of conjugation with the cationic center as the oxime group becomes larger. These rate and computational studies also sugg est that 9-fluorenyl cations are not antiaromatic. They are essentially del ocalized 'nonatetraenyl' cations, where formally antiaromatic resonance for ms contribute little to the overall structure. Copyright (C) 2000 John Wile y & Sons, Ltd.