title: The protonation of gaseous cyclopropane.
abstract: The protonation of cyclopropane by gaseous Brønsted acids of varying strength in radiolytic experiments at atmospheric pressure leads to two distinct C3H7- isomers that have been sampled by their reaction with benzene. The neutral end products, nC3H7-C6H5 and iC3H7-C6H5, arise from the electrophilic aromatic substitution reaction with the cC3H7+ and iC3H7+ ions, respectively. Their relative abundance was studied as a function of pressure, temperature, and the presence of additives in the gaseous systems; the results indicate a large extent of isomerization to the thermodynamically favored iC3H7+ from the protonation by strong acids. The presence of a kinetic barrier prevents any thermal isomerization from taking place in the time frame of 10(-8) s. In the peculiar case in which protonated benzene is the Brønsted acid, C3H7+ ions are formed in the presence of neutral benzene within the same ion - molecule complex. The ensuing reaction shows that cC3H7+ ions are formed exclusively and react in the 10(-10) s(-1) estimated lifetime of the complex. Still, such cC3H7+ ions undergo complete randomization of their hydrogen atoms; this points to a low kinetic barrier for the process. Agreement is found between the reported experimental results and updated computations of the relevant species in the C3H7+ potential energy surface.
authors.affiliation: Dipartimento di Studi di Chimica e Tecnologia delle Sostanze Biologicamente Attive, Università di Roma La Sapienza, Italy.
authors.forename: B
authors.initials: B
authors.lastname: Chiavarino
authors.forename: M E
authors.initials: ME
authors.lastname: Crestoni
authors.forename: A A
authors.initials: AA
authors.lastname: Fokin
authors.forename: S
authors.initials: S
authors.lastname: Fornarini