Hydrogen/chlorine exchange reactions of gaseous carbanions

Gas-phase reactions of three typical carbanions CH₂NO ₂^-, CH₂CN^-, and CH ₂S(O)CH₃^- with the chloromethanes CH ₂Cl₂, CHCl₃, and CCl₄, examined by tandem mass spectrometry, show a novel hydrogen/chlorine exchange reaction. For example, reaction between the nitromethyl anion CH₂NO ₂^- and carbon tetrachloride CCl₄ forms the ion CHClNO₂^-. The suggested reaction mechanism involves nucleophilic attack by CH₂NO₂^- at the chlorine of CCl₄ followed by proton transfer within the resulting complex [CH₂ClNO₂ + CCl₃^-] to form CHClNO₂^- and CHCl₃. Two other carbanions CH₂CN^- and CH₂S(O)CH₃^- also undergo the novel hydrogen/chlorine exchange reactions with CCl₄ but to a much smaller extent, their higher nucleophilicities favoring competitive nucleophilic attack reactions. Proton abstraction is the exclusive pathway in the reactions of these carbanions with CHCl₃. While CH₂CN^- and CH₂S(O)CH₃^- promote mainly proton abstraction and nucleophilic displacement in reactions with CH₂Cl₂, CH₂NO₂^- does not react.