Flow nuclear magnetic resonance detection and characterization of an intermediate on the reaction pathway in a nucleophilic aromatic substitution reaction

Abstract

The use of high resolution flow nmr has made possible the detection and characterization by nmr of the transient intermediate σ-complex on the actual substitution pathway in the nucleophilic aromatic substitution reaction of 1-ethoxy-2,4-dinitronaphthalene (3) with n-butylamine, and the assignment of its uv-visible spectrum. The intermediate is unambiguously identified as the σ-complex (4) and the reaction is one where the two-step mechanism is clearly applicable.

Hydrogen exchange studies. XIV. Kinetics and mechanism of base-catalyzed hydrogen exchange in 1,3-dinitrobenzene in aqueous dimethylformamide and relationship with σ-complex formation

“…A variety of o-complexes which are For personal use only. closely analogous to 3 and 4 have been characterized by nmr as well as uv-vis spectroscopy (1)(2)(3)(4)(5)(6)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22). However, there is as yet no unambiguous uv-vis or nmr evidence for the carbanions 5 and 6.…”

Low-temperature flow NMR investigation of the transient intermediate in the nucleophilic aromatic substitution of 2,4,6-trinitroanisole by n-butylamine

“…In our laboratory we have developed the technique of flow NMR which enables high-resolution NMR spectra to be obtained from flowing chemically reacting mixtures in times as short as 50 ms after mixing.12 It has been successfully applied to the detection and characterization of transient species in several different chemical reactions.13 In particular, it was able to unambiguously characterize the complex observed by Bunnett and Orvik as indeed being species 4. 14 The purpose of the present work was to use this technique in addition to more conventional ones to try to observe and to characterize species of type 1 during a nucleophilic aromatic substitution reaction where the NMR spectra of the species involved would be relatively simple.…”