Observation of an Isolated Intermediate of the Nucleophilic Aromatic Substition Reaction by Infrared Spectroscopy

Abstract

Auf frischer Tat ertappt: Ein σ‐Komplex, der als Zwischenstufe in einer nucleophilen aromatischen Substitution entsteht, wurde im Experiment beobachtet. Die direkte Ionisierung von C6F6 durch kohärente Strahlung im Vakuum‐UV‐Bereich führte über C6F6+/NH3 effizient zu C6F5NH2+. Ein Vergleich des IR‐Spektrums von (C6F6‐NH3)+ mit einem berechneten Spektrum belegt, dass es sich bei dem Kation um einen stabilen σ‐Komplex handelt (siehe Bild).

Aqueous Oxidation of Sulfonamide Antibiotics: Aromatic Nucleophilic Substitution of an Aniline Radical Cation

“…The reaction mechanism presented above resembles that of the (closed‐shell) Smiles‐rearrangement, or, more generally, the mechanism of an aromatic nucleophilic substitution. The latter proceeds via a metastable σ‐complex before breaking the CS bond; this intermediate has been characterized spectroscopically for closed‐shell reactions 29…”

“…Thel atter proceedsv ia am etastable s-complex before breaking the C À Sb ond;t his intermediate has been characterized spectroscopically for closed-shellr eactions. [29] By comparing charges of the C 5 position with computed barrier heights for several hypothetical analogous closedshell reactions,w es how more clearly that the attack is nucleophilic in both the open-shell and closed-shell cases.F or ah ypothetical rearrangement of ac losed-shell species,a nalogous to the reaction undergoneb yS DZC 1 ,w ep ropose Lewis structures,b ased on natural localized molecular orbital (NLMO) analysis (Figure 2c). An electron-withdrawing group (e.g., ÀNO 2 )i npara position to the sulfa moiety enables the rearrangement.…”

Molecular Complexes of Simple Anions with Electron‐Deficient Arenes: Spectroscopic Evidence for Two Types of Structural Motifs for Anion–Arene Interactions

“…[50,51] This approach has allowed valuable information to be gathered on closely related species, such as the positively charged complexes resulting from the interaction of nucleophiles with an electron-deficient aromatic ring or the hydrogen-bonded complexes of halide ions with benzene and fluorobenzenes, which have been characterized by their IR features in the CH and N-H stretch region. [52][53][54][55][56] In a recent communication, the unambiguous structural elucidation of selected Meisenheimer complexes in the gas phase was achieved by examining the fingerprint region of the IR spectrum. [57] The IR features of the TNB-OR À (R = CH 3 , C 2 H 5 ) complexes have been disclosed in the IR multiple-photon dissociation (IRMPD) spectrum reporting the resonance-enhanced photofragmentation process following a multiple-photon absorption in correspondence with the IRactive vibrations of the species.…”