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Reactions of nitroheteroarenes with carbanions: bridging aromatic, heteroaromatic, and vinylic electrophilicity
Authors:Seeliger Florian  Błazej Sylwia  Bernhardt Sebastian  Makosza Mieczysław  Mayr Herbert
Institution:1. Department Chemie und Biochemie, Ludwig‐Maximilians Universit?t München, Butenandtstrasse 5–13, 81377 München (Germany), Fax: (+49)?89‐2180‐77717;2. Institute of Organic Chemistry, Polish Academy of Sciences ul. Kasprzaka 44/52, 01–224 Warsaw, POB 58 (Poland)
Abstract:The relative rate constants for the vicarious nucleophilic substitution (VNS) of the anion of chloromethyl phenyl sulfone (1-) with a variety of nitroheteroarenes, for example, nitropyridines, nitropyrroles, nitroimidazoles, 2-nitrothiophene, and 4-nitropyrazole, have been determined by competition experiments. It was shown that nitropyridines are approximately four orders of magnitude more reactive than nitrobenzene. Among the five-membered heterocycles 2-nitrothiophene is the most active followed by nitroimidazoles and 4-nitropyrazole. Nitropyrroles are the least electrophilic nitroheteroarenes with reactivities comparable to nitrobenzene. Quantum chemically calculated methyl anion affinities (B3LYP/6-311G(d,p)//B3LYP/6-31G(d)) of the nitroarenes correlated only moderately with the partial relative rate constants. The correlation of these activities with the LUMO energies of nitroarenes is even worse. By measuring the second-order rate constants of the addition of 1- to nitroarenes and to diethyl arylidenemalonates 10, it was possible to link the electrophilic reactivities of nitroheteroarenes with the comprehensive electrophilicity scale based on the linear-free-energy-relationship log k(20 degrees C)=s(N+E).
Keywords:aromatic vicarious nucleophilic substitution  density functional calculations  heterocycles  kinetics  linear free energy relationships
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