Theoretical and experimental aspects of the ionisation of carbon acids

• Main Author: Hamdi, Suhaila Talib
• Published: University of Surrey 1977
• Subjects: 547.13
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.457936

This thesis is divided into four chapters. In Chapter 1 the calculation of the acidities of a series of substituted methyl styryl ketones and some miscellaneous carbon acids using a semi-empirical allvalence electron molecular orbital approach is described. Satisfactory correlation is obtained between the calculated and experimental acidities for these molecules. It has also been shown that the order of relative acidities is determined by the facility of negative charge delocalisation in their corresponding carbanions. In Chapter 2 the base-catalysed rates of detritiation of some substituted methyl styryl ketones are reported. The results clearly show that by comparison with the structurally similar acetophenones the interposing of the vinylic linkage in the substituted methyl styryl ketones reduces the effect of the substituent on the hydroxide-catalysed rates of detritiation. In Chapter 3 an account of the synthesis of some substituted benzoylacetones is given. In addition the thermodynamic and kinetic acidities for these 3-diketones have been measured. The primary kinetic isotope ratio k[H]/k[D] values for benzoylacetones are approximately half the k[H]/k[T] values and the Swain-Schaad ratio is close to the expected value of 1. 44. The magnitude of the solvent kinetic isotope effect in the case of anion catalysis is very small (1.22-1.09) and for water catalysis the value is appreciably higher (1.68). In view of the relatively high primary kinetic isotope effects and values near 0. 5 obtained for the Bronsted B parameter a symmetrical transition state is postulated for these B-diketones. In Chapter 4 the rates of detritiation of (alpha-[3]H)-p-dimethylamino-acetophenone in methanolic and ethanolic solutions of potassium, sodium and lithium alkoxides at 25° C are reported. In all the cases considered the alkoxide ion pairs are more reactive than the corresponding free ions. The reactivity of ion pairs follows the order KOR > NaOR > LiOR.