Electrophilic Substitution and Related Reactions

Electrophilic Substitutions and Related Reactions of Furan, Thiophene, Benzofuran, and Benzothiophene. 

The wide variation in the entropy factors for both the substituted phenyl and heterocyclic compounds and in particular for the methoxyphenyl and furan derivatives was considered to be strong evidence for solvent effects being predominant in determining the activation entropy. Consequently, discussion of the substituent effects in terms of electronic factors alone requires caution in this reaction. Caution is also needed since rates for the substituted phenyl compounds were only determined over a 20 °C range. The significance of entropy factors has also been indicated by the poor correlation of the data of the electrophilic reactivities of the heterocyclic compounds, as derived from protodemercuration, with the data for other electrophilic substitutions and related reactions572. 

The Y-T equation (2) has been used extensively in studies of electrophilic substitution in the aromatic ring, and aliphatic nucleophilic substitution and related reactions forming a carbocation or a carbocationic (electron-deficient) centre at the conjugative position (mostly benzylic position) in the side chain. 

The selectivity relationship merely expresses the proportionality between intermolecular and intramolecular selectivities in electrophilic substitution, and it is not surprising that these quantities should be related. There are examples of related reactions in which connections between selectivity and reactivity have been demonstrated. For example, the ratio of the rates of reaction with the azide anion and water of the triphenylmethyl, diphenylmethyl and tert-butyl carbonium ions were 2-8x10 , 2-4x10 and 3-9 respectively the selectivities of the ions decrease as the reactivities increase. The existence, under very restricted and closely related conditions, of a relationship between reactivity and selectivity in the reactions mentioned above, does not permit the assumption that a similar relationship holds over the wide range of different electrophilic aromatic substitutions. In these substitution reactions a difficulty arises in defining the concept of reactivity it is not sufficient to assume that the reactivity of an electrophile is related... 

Volume 8 Volume 9 Volume 10 Volume 12 Volume 13 Proton Transfer Addition and Elimination Reactions of Aliphatic Compounds Ester Formation and Hydrolysis and Related Reactions Electrophilic Substitution at a Saturated Carbon Atom Reactions of Aromatic Compounds Section 5. POLYMERISATION REACTIONS (3 volumes)... 

The use of an electron-rich trivalent phosphorus center for addition to or substitution at an electrophilic site is a long-established approach to the formation of carbon-phosphorus bonds. The classical studies of the Michaelis-Arbuzov, Michaelis-Becker, Abramov, Pudovik, and related reactions and their mechanisms and synthetic utilities have been thoroughly reviewed. In this chapter, we present only a brief introduction to these reactions and provide several examples of their more facile uses from the older literature. More attention is given to relatively recent developments regarding such reactions that are seen as improvements in their general utility. 

After a brief discussion of the notion of molecular topology and the analogy principle as related to topology/reactivity relationships more recent developments in the field of reactivity indices for polynuclear benzenoid hydrocarbons are reviewed. Reaction mechanisms and correlations of reactivity indices with rates of electrophilic substitution and Diels-Alder reactions, thermally induced polymerization, and biochemical transformations of benzenoid hydrocarbons are discussed. 

Because the elementary reactions of cationic alkene polymerizations are directly related to the organic chemistry of carbocations, Chapter 2 will investigate electrophilic additions to double bonds, nucleophilic substitution, electrophilic aromatic substitution, and elimination reactions. 

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