Studies on the effects of substituents on the gas-phase reactions of charged phenyl radicals with allyl iodide, hydrogen atom donors, nitroxides, dienes and small peptides by using mass spectrometry

Jenny Lea Heidbrink, Purdue University

Abstract

This research probes the factors that control radical reactions of charged phenyl radicals in the gas phase by using FT-ICR mass spectrometry. In the first two studies, the ability of differently substituted phenyl radicals to abstract an iodine atom from allyl iodide and a hydrogen atom from tetrahydrofuran and tributyltin hydride was systematically examined. Neutral electron-withdrawing substituents were found to increase the reaction efficiencies by lowering the energy of the transition state. The extent of rate enhancement depends on the type and number of substituents, as well as their location relative to the radical site. Computational results indicate that variations in the transition state energy are explained by polar effects arising from a stabilizing charge transfer resonance structure of the transition state, rather than by variations in the thermodynamic driving force. In the third study, substituent effects on radical-radical recombination reactions were explored. While substituents do not have a major influence on the recombination efficiency, presumably due to a low reaction barrier, the product distribution is greatly impacted. The fourth study focuses on hydrogen atom abstraction and addition-elimination reactions of phenyl radicals with 1,4-cyclohexadiene. The different fragmentation mechanisms of the addition-elimination reactions are discussed. The fifth study examines the effects of the type of the charge site on reactions of substituted phenyl radicals. The results lead to the prediction that neutral phenyl radicals are likely to show similar substituent effect trends. Additionally, the effects of substituents on the reactions of a phenyl radical containing a negative charge site are examined. In the final study, the above approaches were applied to the reactions of phenyl radicals with amino acids and small peptides.

Degree

Ph.D.

Advisors

Kenttamaa, Purdue University.

Subject Area

Analytical chemistry|Organic chemistry|Chemistry

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