Gas-Phase Acid-Induced Nucleophilic Displacement Reactions. 7. Structural and Stereochemical Evidence for the Existence and the Relative Stability of Alkylenebenzenium Ions in the Gas Phase

Article abstract of DOI:10.1021/ja00209a005

A comprehensive investigation on the existence and relative stability of gaseous 2,3-butylene- and 1,2-propylenebenzenium ions was carried out by establishing the structural features and the stereochemistry of acid-induced displacement by CH3OH on isomeric 3-phenylbutyl-2 onium and β-phenylpropyl onium intermediates.The latter were obtained in the gas phase from the reaction of radiolytically formed GA⁺ (GA⁺ = D3⁺, CnH5⁺ (n=1,2), i-C3H7⁺, and CH3FCH3⁺) acids with isomeric 3-phenyl-2-chlorobutanes and β-phenyl-Y-propanes (Y = Cl, OH).The analysis of the isomeric distribution of the neutral substitution products allows the establishment of extensive phenyl-group participation in the displacement process, occuring in competition with methyl and hydrogen 1,2-transfers.The participating ability of a phenyl moiety adjacent to the substitution center is found to depend essentially upon the configuration of the precursor and to be related to its gas-phase nucleophilicity.The occurence of relatively stable cyclic alkylenebenzenium ions as static intermediates in these displacement reactions is suggested by the particular isomeric and stereoisomeric distribution of the products and by its comparison with that obtained from open-chain isomeric ions.The results obtained from the present gas-phase experiments are discussed in the light of those from related gas-phase and solution studies.