Aryloxenium Cations

Purdue University, West Lafayette IN

Investigators

Abstract

In this project supported by the Chemical Structure, Dynamics, and Mechanisms-B (CSDM-B) Program of the Chemistry Division, Professors Hilkka Kenttamaa and John Nash of Purdue University will investigate aryloxenium cations, a broad class of highly reactive compounds, whose chemistry is poorly understood. These cations are the key intermediates in many important chemical and biological reactions, such as the oxidation of phenols and alkanes, the generation of industrial thermoplastics (plastics that do not soften on heating), and the oxidative halophenol dehalogenation by dehaloperoxidase in biology. Oxenium cations have also been implicated in astrochemical studies and are thought to persist in interstellar space. Despite their importance, knowledge on their reactivity is severely limited due to difficulties in generating and studying them in solution. Therefore, although aryloxenium ions have been investigated for more than 40 years, surprisingly little is known about their fundamental chemical reactivity. The information obtained in this research will not only facilitate the rational utilization of aryloxenium cations in organic synthesis and industrial applications but will also enable the design of aryloxenium cations with tailored properties for specific applications. Educational activities in this project will include enhancing the scientific growth of graduate and undergraduate students, including students belonging to underrepresented groups, via a diverse research experience. Hence, this research helps to diversify the STEM workforce. Graduate students involved in this project will participate in industrial or government internships, which not only leads to intellectual broadening but often also to enhanced employment opportunities. These interactions are expected to lead to partnerships with industry and government laboratories, facilitating technology transfer to these laboratories. Detailed kinetic gas-phase reactivity studies on aryloxenium cations will be performed in order to improve the understanding of their chemical properties. Aryloxenium cations are novel species which contain a formally positively charged, monovalent oxygen atom with an incomplete electron shell. In spite of broad fundamental and practical interests in these compounds, relatively little is known about their reactivity. This project will utilize gas-phase ion-molecule reactions performed in ion trap mass spectrometers to explore their chemical properties. Action spectroscopy will be used to verify their structures. Aryloxenium ion reaction products with a variety of different reagents and not just solvents (not possible previously) will be identified. Rates of the reactions of aryloxenium cations will provide detailed kinetic reactivity information that is currently unavailable. The study of the influence of structural changes on the reactivity of aryloxenium cations and the examination of the reactivities of aryloxenium ions with different electronic ground states will facilitate the development of novel reactivity paradigms for aryloxenium cations. The experimental studies will be complemented by high-level quantum chemical calculations in order to deepen our understanding on the observed reactivity. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.