The SN mechanism in aromatic compounds. Part 41. Thermochemical calculations and experimental measurements of methanolysis of 1-fluoro-2,4-dinitrobenzene, picryl chloride, and picryl fluoride

Abstract

Rates and Armenius parameters for methanolysis of 1-fluoro-2,4-dinitrobenzene, picryl chloride, and picryl fluoride have been determined, and shown to be in satisfactory agreement with the results of a fundamental method of thermochemical calculation successfully applied previously to a wide range of S_NAr reactions. These calculations also shed light on the sources of the large difference in nucleophilic strength of OMe^– and MeOH, selected for the comparison of anionic and neutral forms of a nucleophile. The experimental results also lead to a comparison of the leaving group mobility of F and Cl in reactions with MeOH as nucleophile; as well as the activating power of an o-NO₂ group, when there is an NO₂ group in the other ortho-position. In the reaction of picryl chloride, the secondary reaction between product chloride ion and picryl methyl ether (demethylation) was avoided by carrying out the reaction in the presence of silver ion.