Reactivity studies of di- and tridehydropyridine radical cations and analysis of biofuel and petroleum by using fourier transform ion cyclotron resonance and linear quadrupole ion trap mass spectrometry spectrometry

Vanessa A Gallardo Villacis, Purdue University

Abstract

Organic mono- and polyradicals play an important role in a variety of fields including organic synthesis, materials science, and biological activity of organic compounds. Several studies have been published on σ-type carbon-centered mono-, bi- and triradicals. However, σ,σ,σ,σ-tetraradicals have not been investigated experimentally until know. Four organic triradicals were studied in a FT-ICR mass spectrometry in order to enhance the knowledge of σ,σ,σ-triradicals and achieve greater understanding of their reactivity controlling factors. These didehydropyridine radical cations, the carbon-nitrogen (CN) ortho -pyridyne moiety is the same and the third radical site is located at different sites in the pyridine ring. The structures of these triradicals were confirmed by using structurally diagnostic ion-molecule reactions.. An examination of the observed reactivity provides insights into the electronic structure and the most reactive sites of these triradicals wich results indicate the presence of a highly reactive ortho-benzyne moiety in these triradicals, which does not undergo radical reactions. Most of these reactions are thought to be initiated by nucleophilic attack on the C2 position of the benzyne by the neutral reagents. Radical reactions were also observed for these triradicals, abstract an iodine atom form allyl iodide was observed. This observation can be explained by the presence of an unpaired electron in all resonance structures of these triradicals. These triradicals can be viewed as a combination of a reactive ortho-benzyne and a less reactive monoradical. This dissertation report the first reactivity study on an organic σ,σ,σ,σ-tetraradical, the positively charged 2,4,6-tridehydropyridine radical cation, an analogue of the elusive 1,2,3,5-tetradehydrobenzene. The reactivity of the σ,σ,σ,σ-tetraradical is compared to related tri-, bi- and monoradicals in a Fourier Transform-Ion Cyclotron Resonance (FT-ICR) mass spectrometer. Surprisingly, the tetraradical was found not to undergo radical reactions. This behavior is rationalized by resonance structures hindering fast radical reactions. This makes the cation highly electrophilic, and it rapidly reacts with many nucleophiles by quenching the N–C orthobenzyne moiety, thereby generating a relatively unreactive meta-benzyne analogue. In addition to fundamental studies, as described above, mass spectrometry is also an extremely valuable tool in the field of structural elucidation of unknown compounds and analysis of complex mixtures. This dissertation report the utility of the pressure chemical ionization (APCI) and electrospray ionization (ESI) tandem mass spectrometry for MW determination and structural elucidation of oligosaccharides directly without sample pretreatment or derivatization and determination of linkage position of different isomeric disaccharides. All the analytes evaporated and ionized by ESI and APCI with the chloride anion dopant displayed an abundant chloride anion adduct with no fragmentation, including an oligosaccharide with a MW of 1458 Da. CAD of the chloride anion adducts of the sugars studied showed major loss of HCl. This specific loss can be used to verify that the fragmenting ion is a chloride anion adduct, and hence confirm the molecular weight (MW) of the analyte. These experiments, as well as MS3 and MS4 experiments on deprotonated sugars (formed upon loss of HCl from the chloride anion adduct) and their fragmentation products allow distinction of some isomers, including glucose and fructose, sucrose and cellobiose, and laminaripentose and cellopentose. Tandem mass spectrometry was used also for the analysis and study of the fragmentation behavior of protonated molecules and molecular ions derived from molecules in crude oil refinery streams in order to be able to monitor the changes in the composition of refinery streams during processing. This was a joint project between Haldor Topsøe and the Kenttämaa laboratories.

Degree

Ph.D.

Advisors

Kenttamaa, Purdue University.

Subject Area

Chemistry|Analytical chemistry|Organic chemistry

COinS