title: An Experimentally Established Key Intermediate in Benzene Nitration with Mixed Acid.
abstract: Experimental evidence is reported for the first intermediate in the classic SEAr reaction of benzene nitration with mixed acid. The UV/Vis spectroscopic investigation of the reaction showed an intense absorption at 320 nm (appearing as a band shoulder) arising from a reaction intermediate. Our theoretical modeling shows that the interaction between the two principal reactants with solvent (H2SO4) molecules significantly affects the structure of the initial complex. In this complex, a larger distance between the aromatic ring and nitronium ion precludes the possibility for electronic charge transfer from the benzene π-system to the electrophile. The computational modeling of the potential energy surface reveals that the reaction favors a stepwise mechanism with intermediate formation of π- and σ-(arenium ion) complexes.
authors.affiliation: Department of Chemistry and Pharmacy, University of Sofia, Sofia 1164 (Bulgaria).
authors.forename: Gergana
authors.initials: G
authors.lastname: Koleva
authors.affiliation: Department of Chemistry and Pharmacy, University of Sofia, Sofia 1164 (Bulgaria). galabov@chem.uni-sofia.bg.
authors.forename: Boris
authors.initials: B
authors.lastname: Galabov
authors.affiliation: Department of Chemistry and Pharmacy, University of Sofia, Sofia 1164 (Bulgaria).
authors.forename: Boriana
authors.initials: B
authors.lastname: Hadjieva
authors.affiliation: Center for Computational Chemistry, University of Georgia, Athens, GA 30602 (USA). ccq@uga.edu.
authors.forename: Henry F
authors.initials: HF
authors.lastname: Schaefer
authors.affiliation: Center for Computational Chemistry, University of Georgia, Athens, GA 30602 (USA).
authors.forename: Paul von R
authors.initials: Pv
authors.lastname: Schleyer
keywords: aromatic electrophilic substitution; density functional computations; nitration; reaction mechanisms