The protonation of gaseous cyclopropane

The protonation of cyclopropane by gaseous Bronsted 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, nC(3)H(7)-C6H5 and iC(3)H(7)-C6H5, arise from the electrophilic aromatic substitution reaction with the cC(3)H(7)(+) and iC(3)H(7)(+) 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 iC(3)H(7)(+) 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 Bronsted acid, C3H7+ ions are formed in the presence of neutral benzene within the same ion - molecule complex. The ensuing reaction shows that cC(3)H(7)(+) ions are formed exclusively and react in the 10(-10) s(-1) estimated lifetime of the complex. Still, such cC(3)H(7)(+) 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.