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Title: Solvent and structural effects in solvolytic reactions
Author: Norman, S. J.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1993
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Rate Constants for the solvolysis of standard compounds have been used as a measure of solvent polarity. The Grunwald and Winstein equation utilized tert-butyl chloride for the Y scale. YX scales for the 1- and 2-adamantyl derivatives have been established to correlate various substrates with different leaving groups. This thesis presents YOMs results for binary aqueous mixtures of acetonitrile and dioxane which are classified as dipolar aprotic solvents. YCl values have also been obtained. When compounds containing one aromatic ring such as p-methoxybenzoyl chloride are correlated against YCl the plot splits into separate lines for each binary mixture. It is shown that p-methoxybenzyl chloride eliminates this effect because positive charge can be delocalized onto the benzene ring. There is a notably good correlation with Z values: the solvent polarity scale based on the charge transfer absorption band of a pyridinium ion. Free energy relationships like rate-rate profiles can indicate a change in mechanism if a break occurs. This is observed for benzoyl chloride which reacts by a dissociative pathway in highly aqueous media and an addition-elimination pathway in less aqueous media. The compositions of acetonitrile and dioxane where the competing reaction channel contributes 50% to the overall rate have been located and the dissociative channel dissected. The benzhydryl system has been used to provide a rate ratio for tosylates and p-nitrobenzoate leaving groups. The reactive mesylate was prepared on a small scale and transferred to a conductivity cell without isolation. the p-nitrobenzoate was analysed by HPLC which is suitable for much slower reactions. The ratio obtained was compared to previous values for which steric and temperature considerations are important. Also studied were the solvolyses of bicyclo[2.1.1] hexyl and tricyclo[23.1.002,6] hexyl tosylates which proceeded with anchimeric assistance. The corresponding ditosylates had rate constants 3 x 103 smaller in 80% ethanol-water at 25oC mainly due to inductive effects.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available