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The Protonation of Gaseous Cyclopropane
Author(s) -
Chiavarino Barbara,
Crestoni Maria Elisa,
Fokin Andrey A.,
Fornarini Simonetta
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20010702)7:13<2916::aid-chem2916>3.0.co;2-0
Subject(s) - protonation , isomerization , chemistry , cyclopropane , benzene , electrophilic aromatic substitution , ion , photochemistry , computational chemistry , catalysis , medicinal chemistry , organic chemistry , ring (chemistry)
The protonation of cyclopropane by gaseous Brønsted acids of varying strength in radiolytic experiments at atmospheric pressure leads to two distinct C 3 H 7 + isomers that have been sampled by their reaction with benzene. The neutral end products, n C 3 H 7 −C 6 H 5 and i C 3 H 7 −C 6 H 5 , arise from the electrophilic aromatic substitution reaction with the c C 3 H 7 + and i C 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 i C 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 Brønsted acid, C 3 H 7 + ions are formed in the presence of neutral benzene within the same ion–molecule complex. The ensuing reaction shows that c C 3 H 7 + ions are formed exclusively and react in the 10 −10 s −1 estimated lifetime of the complex. Still, such c C 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 C 3 H 7 + potential energy surface.