Effects of the reaction environment on gas-phase proton-induced nucleophilic displacement at saturated carbon1

The H₂O and D₂O chemical ionization (CI) mass spectra of selected methylhalides(CH₃X, XF, CI) have been investigated at source temperatures from 330 to 500°K, and at total pressures from 01 to 1.1 Torr Hydronium (H₃O⁺) ions, the reactant species formed that predominates in our source under these conditions, were found to promote a gas-phase nucleophilic substitution on the halogenated substrate by H₂O, leading to CH₃OH₂⁺ (H₂O)_n (n = 0,1,2) ions. Occurrence of these substitution reactions, which are prevented under ICR conditions, provides direct evidence for contrasting ion reactivities under different experimental conditions, mainly due to the profound influence of the reaction environment on the formation of collision-stabilized intermediate species.