A flowing afterglow study of gas phase carbene thermochemistry
Abstract
The research discussed in this thesis pertains to the thermochemistry of carbenes, and the structure and reactivity of gas-phase halogenated carbanions. The heats of formation of several carbenes have been determined from measurements of the threshold energies for collision-induced dissociation (CID) from $\alpha$-halocarbanions in a flowing afterglow-triple quadrupole apparatus. Also, the gas-phase acidities for various halogenated compounds have been determined from proton transfer bracketing procedures. New values for the heats of formation of all the chloro/fluoro substituted methylenes and selected bromo- and iodocarbenes are given which are compared with previously reported values in the literature. Hitherto unknown values for the heats of formation of methyl-, phenyl-, vinyl-, and cyanocarbene are also presented. The dynamics of $\alpha$-elimination reactions that produce either singlet or triplet carbenes are also described. The CID results for CF$\sb2$Cl$\sp-$, CH$\sb3$OCHCl$\sp-$ and CH$\sb3$SCHCl$\sp-$ suggest the presence of a loosely-bound Cl$\sp-$ in these ions. The chloride affinities in these ions are estimated to be between 8.0 and 12.0 kcal/mol from chloride transfer studies. Thus, these ions are regarded as gas-phase "carbenoids" or carbene/chloride clusters. The CID-based method described in this thesis represents a new tool for obtaining thermochemical information for carbenes. These data are important for understanding the stability of these intermediates, and may ultimately allow the prediction of their reactivity. The method is applicable to a large number of compounds and offers numerous advantages over other appearance energy techniques for determining carbene thermochemistry.
Degree
Ph.D.
Advisors
Squires, Purdue University.
Subject Area
Organic chemistry|Chemistry
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