Competition between Nucleophilic Substitution of Halogen (SNAr) versus Substitution of Hydrogen (SNArH)—A Mass Spectrometry and Computational Study

Abstract The mechanism of intramolecular gas‐phase reactions of N ‐(2‐X‐5‐nitrophenyl)‐ N ‐methylacetamide carbanions (X=H, F, Cl) has been studied using negative ion electrospray mass spectrometry ((−)ESI‐MS) technique and modelled computationally. It was proven that all three anions form cyclic σ H adducts, which undergo elimination of water. In the case of X=F, formation of the σ F adduct, leading to S N Ar reaction, was a competing process. This is the first proof that also in the gas phase formation of σ H adduct proceeds faster than σ X adduct and only when X=F, rates of these two processes are comparable. The experimental results are in full agreement with quantum chemical calculations.