engleski

Determination of nucleofugalities for various benzoates

Solvolytic reactivities of some substituted benzoates in aqueous binary mixtures of ethanol and acetonitrile have been determined experimentally in the terms of nucleofugalities (Nf) according to the three-parameter LFER equation log k (25 °C) = sf (Nf + Ef). This equation is based on the log k vs. Ef correlation, whereat k represents a solvolysis first-order rate constants for benzhydrylium substrates, whereas Ef is the electrofugality parameter of variously substituted benzhydrylium electrofuges. A quantum-chemical model based on the heterolytic dissociation of 2-oxyethyl benzoates has been developed for determining the reactivity of a vast number of benzoates. Experimental ΔG‡ of 13 dianisylmethyl benzoates for solvolysis in aqueous mixtures of ethanol and acetonitrile have been correlated with ΔH‡ of the model epoxy ring formation, calculated by DFT-PCM quantum-chemical method. Along with the excellent correlation (r = 0.997), very good agreement between experimentally derived Nf parameters and calculated Nf parameters have been observed. The method for calculating the nucleofugalities of substituted benzoate leaving groups, which includes the theoretical model, has been established, ultimately providing a possibility for determining the SN1 reactivity for any benzoate in a given solvent.

heterolysis; nucleofugality; benzoates; model; DFT

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