Application of mass spectrometry and nuclear magnetic ressonance for the detection and characterization of key intermediates in organic reactions

Author(s)

Liliane Girotto Cabrini

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Química
• Defense date: 2007-09-02

Examining board members

Marcos Nogueira Eberlin; Adão Aparecido Sabino; Anita Jocelyne Marsaioli; Ljubica Tasic; Roberto Rittner Neto; Sergio Antonio Fernandes

• Advisor: Marcos Nogueira Eberlin

Abstract

This master's thesis is divided in two parts. The first one had the objective to investigate via the NMR technique the reactivity of endo- and exocyclic N-acyliminium ions of 5 and 6 member-rings as a function of ring size, the presence of an aromatic ring and endo or exocyclics acyl groups. For all substracts we observed a deshielding of all the signals in the H-NMR spectra in the presence of Lewis acid. This dishielding was attributed to formation of a Lewis complex. One of such substrates (38) displayed in the H-NMR spectrum an intense singlet at d 9 which was assigned to the methyne hydrogen of the corresponding N-acyliminium ion. This dishielding was also detectable in the C-NMR spectrum (d 171,1). The second part of this thesis describes mass spectrometric (MS) experiments applied in the differentiation of isomers via pentaquadrupole MS, and for the determination of the mechanism of Takeda's olefination via electrospray-MS (ESI/MS). Using ion/molecule reactions of acyl ions (acylpyrrol and acylpiridine) with molecules of different classes such as cyclical acetals, epoxides, nitriles and dienes, it was possible to distinguish the N -, 2- and 3-acylpyrrol and the 2 -, 3- and 4-acylpiridine isomers. The preparation of olefins highly substituted via the carbonyl olefination using gem-dicloro-Cp2Ti[P(OEt)3]2 had been studied by Takeda, and the present ESI-MS results provide insights into its mechanism via the characterization of titanocene and titanocycle intermediates (AU)