Rationalizing the Regioselectivity in Polynitroarene Anionic .sigma.-Adduct Formation. Relevance to Nucleophilic Aromatic Substitution

Abstract

ContentsJuliars Dust completed his B.Sc.(Hons) in 1978 at the University of Waterloo, in southwestern Ontario, but then traveled east to Mt. Allison University, where he studied free radical chemistry of stericaliy-hindered aromatics with Professor Ross Barclay. In 1982 he traveled farther east to Dalhousie University where, under the guidance of Professor Don Arnold, he received a M.Sc. for a thesis that defined the «*n substituent scale for benzylic radicals. Changing direction, Dust moved west to Queen's University, and as a student of Professor Erwin Buncel, commenced a study of Meisenheimer complexes, including those formed by novel ambident polynitroheteroaromatics (i.e. super-electrophiles). This research led to a Ph.D. in 1987 and it continues to be a focus ot his effort. His postdoctoral work at University of Alabama in Huntsville with Professor Milton Harris sparked another continuing interest: preparation, application, and mechanistic investigation ot polyethylene glycol) derivatives. In 1989 he settled in Corner Brook, the western-mosl city in the eastern-most province in Canada, Newfoundland. There he accepted an Assistant Professorship at Sir Wilfred Grenfell College (Memorial University); he was granted tenure in 1994 and was promoted lo the rank of Associate Professor in 1995.

Meisenheimer complexes bonded at carbon and at oxygen

“…As suggested by Buncel [4,8], in polar solvents like DMSO and methanol both C-1 and C-3 regioisomeric Meisenheimer adducts of substituted trinitrobenzenes may be observed for oxygen-centered nucleophiles such as the methoxide ion, depending on the temperature. For carbon-centered nucleophiles such as CH 3 COCH 2 Ϫ , on the other hand, C-3 Meisenheimer adducts are both kinetically and thermodynamically favored.…”

“…Jackson [1] and later isolated by Meisenheimer [2], are anionic -complexes formed by covalent addition of nucleophiles to a ring carbon atom of electron-deficient aromatic and heteroaromatic substrates [3,4]. It is believed that Meisenheimer complexes are key intermediates in nucleophilic aromatic substitution (S N Ar) reactions (Scheme 1).…”

Aromatic nucleophilic substitution (SNAr) Reactions of 1,2- and 1,4-halonitrobenzenes and 1,4-dinitrobenzene with carbanions in the gas phase

“…A romatic nucleophilic substitution (S N Ar) reactions are important from both practical and theoretical point of view [1][2][3][4]. Typical S N Ar reactions (in solution) proceed according to the mechanism shown in Scheme 1.…”

σ-Complexes as biochemical and biophysical probes. Part 6. The interaction of N-2,4,6-trinitrophenyl-L-lysine with methoxide ion in dimethylsulfoxide-methanol (95%-5% v/v) mixture: proton transfer and σ-complex formation

“…[1][2][3] For example, the anti-leukemic activity of certain nitrobenzofurazan and nitrobenzofuroxan derivatives has been linked to the σ -complexes derived in the interaction of these compounds with intracellular thiol groups. 4 Our studies of σ -complexes as biological, biophysical and environmental probes have been multi-pronged [5][6][7][8] .…”

“…Our study 8 of the interaction of the dinitroaniline herbicides, trifluralin and benefin, with hydroxide and sulfite ions has firmly established the formation of anionic σ -adducts by these compounds; structures of the derived species and the pathways for their formation were elucidated. σ-Complexes are recognized as models of the reaction intermediates postulated for nucleophilic aromatic substitution (S N Ar) processes [1][2][3]11,12 . A number of structure-reactivity relationships involving these species have been elucidated; the kinetic and thermodynamic data for the formation and decomposition of the σ-complexes, which have aided the understanding of the mechanism of S N Ar reactions, have been the subject of authoritative reviews [1][2][3] .…”