Electrofugality of Some Ferrocenylphenylmethyl Cations

Sandra Jurić,Olga Kronja,Marijan Marijan

doi:10.5562/cca3553

Abstract

The electrofugality scale has been extended with new substituted ferrocenylphenylmethyl cations 1-4. Ef values were determined by applying the linear free energy relationship (LFER): log k = sf (Ef + Nf). Due to ability of the ferrocene moiety to efficiently stabilize the positive charge, ferrocenylphenylmethyl cations constitute a group of very powerful electrofuges (Ef &gt; 1). Impact of the phenyl group in ferrocenylphenylmethyl derivatives on stabilization of the positive charge is considerably 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. Lack of breakdown of Hammett-Brown plot if the rates for the complete set of substrates 1–5 have been correlated, indicates that the ferrocenyl group in α-position diminishes the stabilizing effects of electron-donating substituents as well.

Highlights

T THE first step in solvolytic SN1 reactions involves the heterolytic cleavage of the carbon—leaving group bond and formation of the carbocation intermediate and the free leaving group.[1]
Log k = sf (Nf + Ef) in which k is first-order rate constant at 25 °C, sf is the nucleofuge-specific slope parameter, Nf is the nucleofugality in a given solvent, and Ef is the independent variable referring to electrofugality
The nucleofuge specific parameters can be derived from log k vs. Ef plots,[4] while the electrofugalities can be derived from log k/sf vs. Nf plots, taking the known sf and Nf parameters

Summary

Introduction

T THE first step in solvolytic SN1 reactions involves the heterolytic cleavage of the carbon—leaving group bond and formation of the carbocation intermediate (electrofuge) and the free leaving group (nucleofuge).[1]. Log k = sf (Nf + Ef) in which k is first-order rate constant at 25 °C, sf is the nucleofuge-specific slope parameter, Nf is the nucleofugality in a given solvent, and Ef is the independent variable referring to electrofugality.

Results

Conclusion