Nucleophilic and Radicaloid Substitution Reactions

Nucleophilic and Radicaloid Substitution Reactions of Monocyclic Thio-phens. - The rate constants for the reaction of 5-substituted 2-bromo-3-nitrothiophens, in methanol, with various substituted anilines to give 5-substituted iV-(3-nitro-2-thienyl)anilines have been measured at various temperatures, It was found that the sensitivity parameters that were obtained from Hammett and Bronsted correlations were practically independent of the starting system. The kinetics of piperidino-substitution of methyl 2-methoxy-3-nitrothiophen-5-carboxylate and 5-acetyl-2-methoxy-3-nitrothio-phen, in which the methoxy-group is the leaving group, have been investigated and the mechanism has been discussed. 

Semenovskii and M. M. Emel yanov, Izv. Akad. Nauk SSSR, Set. Khim., 1981, 

Consiglio, C. Arnone, D. Spinelli, R. Note, and V. Frenna, J. Chem. Soc., Perkin 

Polivka, J. Holubek, E. Svatek, J. Metysovd, and M. Protiva, Collect. Czech. Chem. 

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Nucleophilic and Radicaloid Substitution Reactions of Monocyclic Thiophens. - The kinetics of piperidino- and benzenethiolato-dehalo-genation of some 4-substituted 2,3-dihalogeno-5-nitrothiophens in methanol has been studied at various temperatures. It was found that the activating effect of the 3-halogen-substituent was... 

That is, the act of shifting the single electron from Y to X may occur either with or without free-radical formation. Usually, the concerted non-radicaloid process is energetically favoured. For a more detailed discussion of the various mechanisms of nucleophilic substitution reactions in aliphatic compounds and their solvent dependence, see references [14, 483, 782-785]. 

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