Radical type reactivity of distonic radical cations

Rebecca Lynne Smith, Purdue University

Abstract

Distonic radical cations are species which possess spatially separated charge and radical sites. If the charge site of the distonic ion is chemically inert, reactions may only occur at the remote radical site, thus allowing examination of radical reactions inside a mass spectrometer. Several types of distonic ions were examined in a Fourier transform ion cyclotron resonance mass spectrometer for this purpose and the mechanisms by which they react with many neutral reagents were elucidated. The reactions of a homologous series of acylium distonic ions (i.e., $\rm\sp\cdot CH\sb2(CH\sb2)\sb{n}CO\sp{+};\ n=$ 1-3) were examined to determine if these species behave like neutral radicals. These acylium distonic ions were found, however, to react with neutral reagents via mechanisms involving catalysis by the charge site. The first step in most of the proposed mechanisms involves binding of the neutral molecule to the unsaturated charge site of the ion followed by radical substitution via a cyclic transition state. Since binding between the charge site of the acylium distonic ions and neutral reagents occurs, a distonic ion with a saturated charge site was generated. The ion $\rm(CH\sb3)\sb2S\sp{+}$-CH$\sb2\sp\cdot,$ which contains a coordinatively saturated charge site, was found to react with neutral reagents via pathways that mainly involve the radical site of the ion. However, the adjacent charge site undoubtedly influences the radical reactions through strong electron-withdrawing effects. To overcome the problems associated with the acylium distonic ions and $\rm(CH\sb3)\sb2S\sp{+}$-CH$\sb2\sp\cdot,$ distonic ions with saturated charge sites separated from the radical site by a phenyl ring (charged phenyl radicals) were examined. These charged phenyl radicals were found to react with reagents such as dimethyl disulfide analogously to neutral radicals. The charge site of these species was found to influence the reactions at the radical site only through electron-withdrawing effects. Thus, these charged phenyl radicals will allow for the examination of radical reactions inside a mass spectrometer.

Degree

Ph.D.

Advisors

Kenttamaa, Purdue University.

Subject Area

Chemistry|Analytical chemistry

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