Gas-phase reactivity studies of biradicals related to drug intermediates in a FT-ICR mass spectrometer

Frances Amegayibor, Purdue University

Abstract

This thesis describes a systematic examination of the chemical properties of a series of isomeric protonated didehydroarenes (didehydroquinoliniums and -isoquinoliniums) and the monoradical analogues by using Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR). The ortho-benzyne and meta-benzyne derivatives with large singlet-triplet (S-T) gaps were found to react by nonradical addition/elimination pathways. A comparative study of two isomeric ortho-benzyne derivatives showed that an increase in electrophilicity leads to an enhancement in the addition reaction rate. One para-benzyne derivative was studied, and it appears to be a weaker electrophile but more reactive radical than the meta -isomer. Another study that involved an examination of the radical reactions of the para-benzyne derivative and three other didehydroarenes also with a 1,4-relationship revealed that electronic effects due to singlet-triplet (S-T) gap, can sometimes be offset by polar effects. As a consequence of the proximity and orientation of its formally singly occupied molecular orbitals, the biradical 4,5-didehydroisoquinolinium with nearly degenerate singlet and triplet states, was found to react by addition as well as radical pathways. Finally, the results of the ion-molecule reactions used to characterize a novel σ,π-biradical, N-methylene-5-dehydroisoquinolinium, is described.

Degree

Ph.D.

Advisors

Kenttamaa, Purdue University.

Subject Area

Analytical chemistry|Organic chemistry

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