Gas-Phase Acid-Induced Nucleophilic Displacement Reactions. 4. A Stereochemical Probe for the Existence and the Relative Stability of Cyclic Halonium Ions in the Gas Phase

Article abstract of DOI:10.1021/ja00403a029

A comprehensive investigation on the existence and the relative stability of gaseous three-membered cyclic butene halonium ions was carried out by establishing the stereochemistry of the acid-induced displacement by nucleophilic such as H2O, H2S, etc., on a number of positively charged intermediates.The latter were obtained in the gas phase from the reaction of radiolytic formed Broensted (CH5⁺ and C2H5⁺) and Lewis (C2H5⁺ and CH3FCH3⁺) acids with 2,3-dihalobutanes.The stereoisomeric distribution of the neutral 3-halobutan-2-ols (or thiols) formed in these processes strongly implies the intermediacy of cyclic 2,3-butene halonium ions, whose stability in the gas phase depends on the nature of the halogen involved, increasing in passing from Cl to Br.No evidence for the occurrence of stable cyclic 2,3-butene fluoronium ions was obtained by the same procedure.Other factors, namely the strength of the radiolytic gaseous acid "catalysts" and the configuration of the starting dihalobutane, were found to play a role in determining the stereochemistry of the substitution processes investigated.A close correspondence does exist between the present results and those from strictly related mass spectrometric and condensed phase investigation.