engleski

Nucleofugalities of butyrate and isobutyrate in various solvents

Nucleofugalities (the leaving group abilities) of butyrate and isobutyrate in various aqueous protic and aprotic solvents have been derived from the SN1 solvolysis rate constants of the corresponding X-benzylferrocenyl derivates by applying the LFER Equation: log k = sf (Ef + Nf). In this equation k is a first order rate constant for SN1 reaction at 25°C, sf (slope of the log k/Ef correlation line) and Nf (nucleofugality, negative intercept on the abscissa of the log k/Ef correlation line) are nucleofuge specific parameters, while Ef is the electofugality parameter of the corresponding benzylferrocenyl electrofuge determined earlier. Comparison with neutral and other anionic leaving groups reveals that butyrate and isobutyrate are relatively poor leaving groups, whose nucleofugalities (Nf values) are similar with the nucleofugalities of pyridine and its 4-substituted derivates, benzoate, and acetate. Also, it has been found that the Nf values of butyrate in all examined solvents are slightly higher than Nf values of isobutyrate.

Nucleofugality ; solvolysis rate ; butyrate ; isobutyrate

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