The Gas-Phase Ion Chemistry of Substituted Silanes

Citation

Murthy, Srihari (1993) The Gas-Phase Ion Chemistry of Substituted Silanes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/8gv5-xy57. https://resolver.caltech.edu/CaltechTHESIS:01042013-113332582

Abstract

Ion-molecule reactions in the chlorosilanes, SiH_nCl_4-n (n = 0-3), and in phenylsilane have been studied by the technique of Fourier transform ion cyclotron resonance spectrometry.

In Chapter 1, the motivations for studying the gas-phase ion chemistry of substituted silanes as well as brief descriptions of the gas phase ion chemistry of the chlorosilanes and of phenylsilane are presented.

Chapter 2 deals with the gas-phase ion chemistry of the chlorosilanes, SiH_nCl_4-n (n = 0-2). Reactions of the chlorosilyl ions with neutral chlorosilanes and with silane as well as the reactions of the silyl ion with neutral chlorosilanes are presented. The chlorosilyl ions participate in Hˉ, Clˉ transfer reactions and disproportionation reactions. The mechanisms of these reactions are discussed. The Clˉ affinities of the chlorosilyl ions, SiH_nCl_3-n⁺ (n = 0-2), lie within a range of 1.2 kcal mol^-1 and decrease in the order SiH₂Cl⁺ > SiHCl₂⁺ ≈ SiCl₃⁺. The heats of formation of the chlorosilyl ions are determined.

Chapter 3 deals with the gas-phase ion chemistry of monochlorosilane. The difference in the Hˉ affinities of the ions SiH₂Cl⁺ and SiHCl₂⁺ is determined to be 1.5 ± 0.3 kcal mo^-1. The Hˉ affinities of the chlorosilyl ions, SiH_nCl_3-n⁺ (n = 0-2), lie within a range of 1.8 kcal mol^-1 and decrease in the order SiHCl₂⁺ ≈ SiCl₃⁺ > SiHCl₂⁺. Protonated SiH₃Cl is generated by proton transfer from CH₅c and is observed to react with SiH₃Cl to yield (SiH₃)₂Cl⁺.

Chapter 4 deals with the gas-phase ion chemistry of phenylsilane. In analogy with toluene, two (parent – H)⁺ cations are produced by the electron impact ionization of phenylsilane. These cations are identified to be the phenylsilyl and the silacycloheptatrienyl cations.

Chapter 5 explores the gas-phase ion chemistry of phenylsilane in great detail. Reactions of the parent and fragment ions (created by electron impact ionization) with neutral phenylsilane and with C₆D₆ are presented. Two structural isomers are identified for the C₆H₈Si⁺ cation and three structural isomers are identified for the C₆H₆Si⁺ cation. The Hˉ affinity of the phenylsilyl cation is also presented.

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