Gas-phase reactions of three typical carbanions CH₂NO₂⁻, CH₂CN⁻, and CH₂S(O)CH₃⁻ with the chloromethanes CH₂Cl₂, CHCl₃, and CCl₄, examined by tandem mass spectrometry, show a novel hydrogen/chlorine exchange reaction. For example, reaction between the nitromethyl anion CH₂NO₂⁻ 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.