Stereospecific Ion-Molecule Reactions of Nucleophilic Gas-phase Reagents with Protonated Bifunctional Tetracyclic Terpene Epimers in the Triple Quadrupole Collision Cell
✍ Scribed by Cole, Richard B.; Tabet, Jean-Claude
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 423 KB
- Volume
- 32
- Category
- Article
- ISSN
- 1076-5174
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✦ Synopsis
Various nucleophilic reagents (methanol, acetone, ammonia and trimethylamine), characterized by di †erent proton affinities, were introduced into the collision cell of the triple quadrupole as reactive gases for collisionally activated reaction (CAR) studies on stereoisomeric tetracyclic terpenes containing acetal and cyclobutanol functions. Under low-energy and multiple collision conditions, proton transfer from protonated terpenes (MH', selec-(E lab ¿ 3 eV) ted by the Ðrst quadrupole) to the reagent gas was observed in each case, at varying efficiencies. At the same time, collision-induced decompositions (CIDs) were observed as competing processes in each tandem mass spectrum. For methanol, the reaction gas having the lowest proton affinity, CID processes were heavily favored, whereas CAR processes dominated only for trimethylamine (highest proton affinity) reacting with the exo terpene epimer. The latter reagent gas receives the proton in an exothermic transfer which is strikingly stereospeciÐc. The underlying stereochemical e †ect is attributed not only to proton affinity di †erences which favor transfer from the exo epimer, but also to steric and kinetic factors which are evidently highly unfavorable for the endo conÐguration.
1997 by ( John Wiley & Sons, Ltd.