title: Arenium ions are not obligatory intermediates in electrophilic aromatic substitution.
abstract: Our computational and experimental investigation of the reaction of anisole with Cl2 in nonpolar CCl4 solution challenges two fundamental tenets of the traditional SEAr (arenium ion) mechanism of aromatic electrophilic substitution. Instead of this direct substitution process, the alternative addition-elimination (AE) pathway is favored energetically. This AE mechanism rationalizes the preferred ortho and para substitution orientation of anisole easily. Moreover, neither the SEAr nor the AE mechanisms involve the formation of a σ-complex (Wheland-type) intermediate in the rate-controlling stage. Contrary to the conventional interpretations, the substitution (SEAr) mechanism proceeds concertedly via a single transition state. Experimental NMR investigations of the anisole chlorination reaction course at various temperatures reveal the formation of tetrachloro addition by-products and thus support the computed addition-elimination mechanism of anisole chlorination in nonpolar media. The important autocatalytic effect of the HCl reaction product was confirmed by spectroscopic (UV-visible) investigations and by HCl-augmented computational modeling.
authors: Department of Chemistry and Pharmacy, University of Sofia, Sofia 1164, Bulgaria; galabov@chem.uni-sofia.bg ccq@uga.edu schleyer@uga.edu.
authors: Boris
authors: B
authors: Galabov
authors: Department of Chemistry and Pharmacy, University of Sofia, Sofia 1164, Bulgaria;
authors: Gergana
authors: G
authors: Koleva
authors: Institute of Organic Chemistry with Centre of Phytochemistry, Laboratory Nuclear Magnetic Resonance, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria; and.
authors: Svetlana
authors: S
authors: Simova
authors: Department of Chemistry and Pharmacy, University of Sofia, Sofia 1164, Bulgaria;
authors: Boriana
authors: B
authors: Hadjieva
authors: Center for Computational Quantum Chemistry and Department of Chemistry, University of Georgia, Athens, GA 30602 galabov@chem.uni-sofia.bg ccq@uga.edu schleyer@uga.edu.
authors: Henry F
authors: HF
authors: Schaefer
authors: Center for Computational Quantum Chemistry and Department of Chemistry, University of Georgia, Athens, GA 30602 galabov@chem.uni-sofia.bg ccq@uga.edu schleyer@uga.edu.
authors: Paul von Ragué
authors: Pv
authors: Schleyer
keywords: alternative computed routes; autocatalysis; organic chemistry; reaction mechanisms