Degree Type

Dissertation

Date of Award

1987

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Thomas J. Barton

Abstract

In an attempt to generate allene via a thermally-induced [beta]-elimination of methoxytrimethylsilane, flash vacuum pyrolysis (FVP) of 1-methoxy-2-trimethylsilyl-2-propene was found to give isopropenyltrimethylsilane via a retro-ene elimination of formaldehyde. By rendering the retro-ene process unavailable through replacement of the methoxy group by a trimethylsiloxy group, [beta]-elimination of hexamethyldisiloxane was found to be a viable route to allenes;An attempt to generate 1,1-dimethyl-1-silaallene by pyrolytic elimination of methoxytrimethylsilane from (1-trimethylsilyl)vinyldimethylmethoxysilane led to the discovery that vinyldimethylalkoxysilanes extrude dimethylsilanone via an unprecedented homolytic 1,5-migration of hydrogen to form a 1,4-biradical. Other mechanistic possibilities including an initial 1,2-migration of silicon to generate a carbene, a homolytic loss of methyl group, and a retro-ene elimination of formaldehyde to form a silene, were ruled out on the basis of product analysis, isotope labeling, and kinetic investigations. Dimethylsilanone was also generated by a retro-ene decomposition of allyloxydimethylsilane. Substitution by two methyl groups at the allylic position of allyloxydimethylsilane was found to give rise to a competition between the retro-ene process and a homolytic cleavage of the C-O bond to form the highly stable 2-methyl-2-butenyl radical;FVP of (1-methoxyethenyl)pentamethyldisilane was found to generate vinylidene via an [alpha]-elimination of methoxypentamethyldisilane rather than generating 1,1-dimethyl-1-silaallene via a much more thermodynamically favorable [beta]-elimination of methoxytrimethylsilane. A detailed gas-phase kinetic investigation using simple model systems revealed that [alpha]-eliminations of alkoxysilanes to generate carbenes were favored over [beta]-eliminations of alkoxysilanes to generate silenes and olefins, due to entropically favored three-centered transition states for [alpha]-eliminations over four-centered transition states for [beta]-eliminations.

DOI

https://doi.org/10.31274/rtd-180813-11694

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Sukhamaya Bain

Language

en

Proquest ID

AAI8805044

File Format

application/pdf

File Size

123 pages

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