Contributions to the Interpretation of Mass Spectra of the TEOS Methoxy-Transesters. Linked Scans, Accurate Mass Measurements and M+1, M+2 Isotopic Effects

Virgil Badescu

doi:10.37358/rc.20.8.8277

Abstract

The aim of this article is the study of the fragmentation reactions of the methoxy-transesters of tetraethoxysilane (TEOS), with structural formula (CH3O)x(C2H5O)ySi, initiated by electronic impact in the ionization chamber of a double focusing mass spectrometer. The initiation centers of fragmentation reactions for the neutral and ionized TEOS methoxy-transesters were established by quantum calculations of net atomic charges. The ions of the mass spectra of the TEOS methoxy-transesters were obtained experimentally by the B/E and B/E(1-E)1/2 linked scans. Thus, there can be written the fragmentation pathways for the primary events by B/E linked scan (cleavage of methoxy and ethoxy groups) and eliminations of neutral molecules (acetaldehyde, ethylene, formaldehyde, molecular hydrogen) by B/E(1-E)1/2 linked scan. Accurate mass measurements at high resolution (5000), double bond equivalent (DBE) for the molecular ions and fragmentation ions of the TEOS methoxy-transesters and M+1, M+2 isotopic effects were used to confirm their identification. The reaction pathways and accurate mass in mass spectrum of dimethoxydiethoxysilane (TR2M) are detailed.

Highlights

The first purpose of the author thesis [1] was the separation and identification of molecular species obtained in the sol-gel process by gas chromatography coupled with mass spectrometry (GC-MS)
The second purpose of the author thesis [1] was the development of a procedure for the interpretation of mass spectra of some silicon alkoxides and their transesters and oligomers obtained by the sol-gel process
The relationship between the chemical structure of the molecules and their mass spectra has been highlighted by Lafferty [11]; according to his theory the relative intensity of fragmentation ions is determined by the stability of the reaction products and of the bond strength

Summary

Introduction

The first purpose of the author thesis [1] was the separation and identification of molecular species obtained in the sol-gel process by gas chromatography coupled with mass spectrometry (GC-MS). The second purpose of the author thesis [1] was the development of a procedure for the interpretation of mass spectra of some silicon alkoxides and their transesters and oligomers obtained by the sol-gel process. The relationship between the chemical structure of the molecules and their mass spectra has been highlighted by Lafferty [11]; according to his theory the relative intensity of fragmentation ions is determined by the stability of the reaction products and of the bond strength. A complementary theory has been developed by Djerassi [12]; according to his theory, the charge and radical localization after ionization contributes to establish the initiation centers of the fragmentation reactions

Objectives

Methods

Results

Conclusion