Tuning the Reactivity of ortho-, meta- and para- Benzyne Analogs and Releated Polyradicals in the Gas Phase

Purdue University, West Lafayette IN

Investigators

Abstract

Experimental reactivity studies on organic bi- and polyradicals are hindered by the difficulty of generating them cleanly in solution, in addition to their high reactivity and short lifetime. Information on the factors that control the chemical properties of carbon-centered sigma-type biradicals, such as the benzynes and their analogs, is highly desirable since it may allow one to "tune" their reactivity by varying structural details, and hence design bi- and polyradicals with tailored properties. This research program uses the "distonic ion approach" to study the reactivity of gaseous, carbon-centered, sigma-type mono-, bi- and triradicals via their charged analogs by using Fourier-transform ion cyclotron resonance mass spectrometers, a flowing afterglow quadrupole-octapole-quadrupole apparatus, and most recently, a linear quadrupole ion trap. These studies have demonstrated that the electron affinity and singlet-triplet gap of biradicals, as well as dehydrocarbon atom separation for meta-benzyne analogs, are among the reactivity controlling factors that can be used to "tune" the reactivity of some of these species. However, only few different ortho- and meta-benzyne analogs, and most remarkably, no para-benzyne analogs, have been studied thus far. Hence, this research will now be extended to several different and differently substituted ortho- and meta-benzyne analogs. With the means to generate para-benzyne analogs in the gas phase, an examination of their reactions is planned. Finally, the factors that control the reactivity of related tri- and tetraradicals will also be explored. The ability to predict, control and rationalize the outcomes of chemical reactions frequently requires knowledge of key reaction intermediates. Aromatic compounds that carry one (monoradicals) or more unpaired electrons (polyradicals) play an important role, for example, in organic synthesis and the biological activity of organic compounds. This research focuses on improving fundamental understanding of the chemical properties of these reactive intermediates. Ultimately, this research will lead to improved methods to synthesize new organic compounds, including drugs and new materials, as well as more rational design of new drugs. The new experimental methodologies developed here for the characterization of reaction intermediates will have an impact on experimental physical and physical organic chemistry. The broader societal impacts and enhancement of infrastructure include a large number of ethnically diverse, highly qualified science Ph.D. candidates, improved methodology for chemical analysis of organic compounds (including petroleum), and a more solid knowledge base for the design and synthesis of new organic materials and drugs.