Part I. The effects of gamma and delta group IVA metalloidal substituents on rates of carbocation formation. Part II. Modernization of the bipolar pulsed conductance instrument.

摘要

The first part of this dissertation investigates the effects of ;The solvolysis of 4-trimethylsilyl-2-chloro-2-methylbutane and its carbon analog, 2-chloro-2,5,5-trimethylhexane, in aqueous ethanol and aqueous 2,2,2-trifluoroethanol has been examined. In contrast to the secondary system 4-trimethylsilyl-2-butyl 4-bromobenzenesulfonate, in which the intermediate carbocation is strongly stabilized by percaudal participation (overlap of the back lobe of the Si-C bond with the developing p orbital), the tertiary system is seen to solvolyze with only a small extent of participation, with participation preferred in trifluoroethanol.;The isotope effects for the solvolyses of ;The solvolyses of 4-trimethylsilyl-2,2-dimethylbutyl pentafluorobenzenesulfonate, its carbon analog, 2,2-dimethylbutyl pentafluorobenzenesulfonate, and 5-trimethylsilyl-3,3-dimethyl-2-pentyl 4-bromobenzenesulfonate in aqueous trifluoroethanol have been examined to determine the extent of the migratory aptitude of the trimethylsilylethyl group. Only a very slight statistical preference for trimethylsilylethyl migration was seen for 4-trimethylsilyl-2,2-dimethylbutyl pentafluorobenzenesulfonate. It is concluded that this system involves rate-determining formation of the tight-ion pair with a small extent of participation by the migrating group, with only a slight degree of bond-breaking at the migration origin. A preliminary rate constant for the solvolysis of 5-trimethylsilyl-3,3-dimethyl-2-pentyl 4-bromobenzenesulfonate indicates a rate acceleration compared to 3,3-dimethyl-2-butyl 4-bromobenzenesulfonate which appears to be larger than would be expected for simple alkyl substitution.;The second part of the dissertation involves a description of hardware and software improvements made to the bipolar pulsed conductance instrument. A brief introduction to the conductance technique is given, followed by details about the specific hardware and software changes implemented. The modifications made allow conductometric rate constants to be determined with greater speed and precision.