Gas-phase acid-induced nucleophilic displacement reactions. 5. Quantitative evaluation of neighboring-group participation in bifunctional compounds

The mechanism and major paths for the gas-phase nucleophilic displacement on several classes of pos. charged intermediates, formed from the attack of gaseous acids (CH5+, Et+, Me2F+, etc.) on suitable substrates, is discussed. The anal. of the stereoisomeric distribution of the neutral end products allows a quant. evaluation of the gas-phase neighboring-group participation in such systems. A participating-group ability trend of OH » Br ≥ Cl is found, which is appreciably dependent on the nature of the leaving group and the configuration of the starting substrate. The evaluation of the adjacent-group effective concns. in these gaseous systems provides the first direct evidence for a gas-phase anchimerically assisted ionic reaction, involving a 3-membered ring formation. The results obtained in the gas phase differ significantly from those concerning related solvolytic processes.