Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.776726
Title: The enolisation of some diaroylmethanes and the acylation of their metal chelates
Author: Murray, Michael Gerard
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1964
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Abstract:
A study of the structures of the isoxazoles derived from a series of diaroylmethanes has shown that the enolic form of these diketones contains a high degree of electron delocalization within the chelated ring. Partial charge localisation is effected by aryl substitutents whose inductive and mesomeric effects act in the same direction, and one carbon-oxygen bond exclusively has carbonyl character. When the inductive and mesomeric natures of the substitutents are mutually opposed, the enol behaves as a mixture of tautomers, and both carbon oxygen bonds have double bond character. In an extension of a previous investigation of the mechanism of acylation of B-diketone metal chelates, the importance of the electronic nature of the ligand has been clarified. As the electron-affinity and acidity of the parent diketone increases, so the proportion of C-substitution occurring in the acylation of the chelates, is found to decrease. The observations have confirmed that metal of the chelate, permitting the formation of cyclic transition intermediates which yield the triketone and ester products. When the metal is incapable of being coordinated by the reagent, reaction proceeds by an ionic process, and a high proporation of ester results, which is relatively independent of the ligand substituents. Reaction of the diketones with benzoyl chloride in pyridine yielded only one ester, whereas two isomers are theoretically possible. The same single product was isolated from the reactions of the diketone chelates. This selectivity of attack has been attributed to the participation of the enolate anion in the direct esterification of the diketone, and to asymmetry in the metal-oxygen bonding in the chelates. Physical evidence of an interaction between pyridine and the diketones has been observed, and this is believed to give rise to the anion in the reaction. The more stable anion, dictated by that conjugation which gives the greater loss in potential energy, is exclusively formed. Previous evidence has discounted the possibility of an ionic esterification of the chelate, and bond asymmetry, at least in the transition stage of the reaction, is envisaged as an explanation of the selectivity of the position of attack.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.776726  DOI: Not available
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