engleski

ELECTROFUGALITIES AND SOLVOLYTIC BEHAVIOR OF SOME FERROCENYLPHENYLMETHYL CATIONS

Previous kinetic studies established that the ferrocenyl group in α-position to the reaction center considerably enhances the SN1 solvolytic reactivity of the ferrocenylphenylmethyl substrate. These investigations have now been extended to determine electrofugalities of new substituted ferrocenyl-phenylmethyl derivates by applying the linear free energy relationship (LFER) equation: log k = sf (Ef + Nf).The carbocation (electrofuge) is characterized here by a single, solvent-independent parameter Ef whereas the couple consisting of the leaving group and the solvent is characterized by the two parameters Nf and sf. Taking those earlier determined sf and Nf parameters, the electrofugality parameter Ef of a given electrofuge can be derived from log k/sf versus Nf plots. Due to ability of the ferrocene moiety to efficiently stabilize positive charge, ferrocenylphenylmethyl cations constitute a group of very powerful electrofuges (Ef > 1) in comparison with similar benzhydrylium electrofuges. Furthemore, impact of the phenyl group in ferrocenylphenylmethyl derivatives on stabilization the positive charge is somewhat leveled by the ferrocenyl group, so the rate effect of the alkyl substituents (methyl, ethyl, and tert-butyl) on the phenyl ring is suppressed, causing narrow range of Ef parameters.

Electrofugality ; nucleofugalty ; ferrocenylphenylmethyl cation ; solvolysis ; substituent effect

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