Synthesis and reactivity of charged aromatic mono- and biradicals inside a Fourier-transform ion cyclotron resonance mass spectrometer
Abstract
The chemistry of aromatic radicals and biradicals has received much attention in recent years due to the proposition that the action of several antitumor and antiviral drugs is based on hydrogen atom abstraction by substituted aromatic (bi)radicals. The rational design of synthetic versions of such drugs could be greatly enhanced by systematic studies of substituent effects on the reactions of aromatic radicals and biradicals and the various factors that control biradical reactivity. Thus, we developed a method whereby reactions of charged analogs of aromatic radicals and biradicals can be explored by using FT-ICR mass spectrometry. Examination of the effects of neutral substituents on the reactions of charged phenyl radicals suggests that electron-withdrawing substituents greatly enhance the reactivity of these species toward various atom and group donors through polar effects. We also generated a meta-benzyne biradical bearing a charged substituent. This species exhibits reactions characteristic of both its ortho-benzyne and phenyl radical counterparts. These reactions were slower, however, than those of the charged phenyl radical or ortho-benzyne. The addition reactions typical of ortho-benzyne are hindered by the greater distance between the radical sites of meta-benzyne, while the radical reactions of meta-benzyne likely proceed slowly due to its large singlet-triplet gap. In contrast, biradicals with a singlet-triplet gap near zero undergo radical reactions as fast as the related monoradicals. A hydroxy-substituted meta-benzyne located on a protonated quinoline undergoes radical reactions more readily than its unsubstituted counterpart. Charged analogs of para-benzyne undergo facile ring-opening in the gas phase. A substantial amount of additional research pertaining to the work discussed in this thesis has been performed, and the recent literature should be referred to for updated information.
Degree
Ph.D.
Advisors
Kenttamaa, Purdue University.
Subject Area
Analytical chemistry|Organic chemistry
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