Ions acilio : estrutura e reatividade na fase gasosa

AUTOR(ES)

Luiz Alberto Beraldo de Moraes

DATA DE PUBLICAÇÃO

1999

RESUMO

The structure and reactivity in the gas phase of several acylium ions ( R-CO ) and their sulfur analogues were studied using pentaquadrupole mass spectrometry. Cyclic ionic ketal were formed via ketalization reactions of acylium ions with diols and analogues; the products were characterized via sequential MS spectra and isotopic labeling with R-C=O. The dissociation of O-labeled ionic ketal occurred via re-generation of both the labeled and unlabeled reactant acylium ion in equal abundance s, and this dissociation pattern characterized cyclic and O/O-scrambled structures. Acylium and thioacylium ions also reacted with cyclic ketals and acetals via transacetalization, by which the protected carbonyl compound is replaced by the reactant acylium ion. For O/S-cyclic ketals, the sulfur site is the most reactive. Acylium ions were also found to promote ring expansion of epoxide rings (the gas-phase "Meerwein reaction") forming cyclic ionic ketals. However, heterocyclic rings of five and six members failed to undergo similar reactions with acylium ions, likely owing to reduced ring strain. Structural characterization of the ionic products as cyclic ionic ketals were also performed by using R-C=O. The gas-phase ketalization, transacetalization and epoxide ring expansion reactions were used to characterize the acylium site in distonic acylium ions, diacylium ions and isomers differentiation of the benzoyl cations; they provide structurally diagnostic tests for gaseous acylium ions. Ab initio and DFT calculations showed that the novel reactions observed for acylium ions in the gas phase are thermodynamically favored, providing therefore theoretical support for the experimental results.

ASSUNTO(S)

reações quimicas espectrometria de massa

Documentos Relacionados

• Sintese, estrutura, reatividade e propriedades de ions convencionais, distonicos e não-classicos na fase gasosa
• Estudo da formação, estabilidade e reatividade de ions na fase gasosa atraves de espectrometria de massas pentaquadrupolar e calculos teoricos de orbitais moleculares
• Estudo da reatividade de ions e moleculas por colisões dissociativas e reações ion-molecula em fase gasosa via espectrometria de massas pentaquadeupolar
• O uso de auxiliares quirais cicloexilicos na adição de nucleofilos a ions N-aciliminios ciclicos : a reação de aliltrimetilsilano com ions iminios e N-aciliminios em fase gasosa
• Utilização da fotocatalise heterogenea na destruição do cianeto : fase gasosa x fase aquosa