Substituent effect, additivity

Substituent effect, additivity of, 570 electrophilic aromatic substitution and, 560-563 summary of. 569 Substitution reaction, 138 Substrate (enzyme), 1041 Succinic acid, structure of, 753 Sucralose, structure of. 1006 sweetness of, 1005 Sucrose, molecular model of. 999 specific rotation of, 296 structure of, 999 sweetness of, 1005 Sugar, complex, 974 d, 980 L, 980... 

Styrenes—see Hydroxystyrenes Substituent effects, additivity of 263, 899 Sugars—see 1-Acetylsugars, Cahxsugars Sulfides, asymmetric oxidation of 699 Sulfinyl derivatives, formation from thiacalixarenes 1415... 

The question then arises What choice of method for the evaluation of substituent constants should be made. The disadvantage of the reference set method is the question of the validity of the reference set chosen that is, is it the best model for a particular kind of substituent effect In our opinion, when there is a good chemical reason for the choice of a reference set, and sufficient data are extant, this method is perferable. Furthermore, as noted previously, secondary values should be calculated only from those additional sets which by virtue of the known similarity of their structures to that in the defining standard set can be expected to exhibit similar substituent effects. Additionally, such secondary sets should have been studied under comparable reaction conditions. Thus, Charton (40) in the evaluation of the u steric parameters, first demonstrated that acid catalyzed ester hydrolyses are in fact linearly related the u parameters for groups of known van der Waals radii, ryx. This reaction could therefore be used to determine apparent v values for unsymmetric substituents, for... 

Boron trichloride, usually in conjunction with an additional Lewis acid, effects o-chloroacetylation of anilines. The resulting products are converted to indoles by reduction with NaBH4.[l], The strength of the Lewis acid required depends upon the substitution pattern on the ring. With ER substituents no additional... 

In addition to steric effects, there are other important substituent effects which determine both the rate and mechanism of nucleophilic substitution reactions. It was... 

The very high levels of head addition and the substituent effects reported in these studies are inconsistent with expectations based on knowledge of the reactions of small radicals (see 2.3) and are at odds with structures formed in the intermolecular step of cyclopolymerization of diallyl monomers (see 4.4.1.1) where overwhelming tail addition is seen. 

However, measurements of substituent effects supported the hypothesis that the aryl cation is a key intermediate in dediazoniations, provided that they were interpreted in an appropriate way (Zollinger, 1973a Ehrenson et al., 1973 Swain et al., 1975 a). We will first consider the activation energy and then discuss the influence of substituents, as well as additional data concerning the aryl cation as a metastable intermediate (kinetic isotope effects, influence of water acitivity in hydroxy-de-di-azoniations). Finally, the cases of dediazoniation in which the rate of reaction is first-order with regard to the concentration of the nucleophile will be critically evaluated. 

Similar correlations of orbital interactions with substituent effects were also found in additions of alkenes to substituted carbenes and of N2 to transition metal complexes (see Zollinger, 1983 b, 1990). 

Shono et al. (1979) describe a method for hydro-de-diazoniations which is simple, gives excellent yields, and is claimed to show no unfavorable substituent effects (14 examples). It consists of the addition of thiophenol (7 equiv.) to a suspension of an arenediazonium tetrafluoroborate in a mixture of water and pentane (10 1) at room temperature. After the completion of N2 evolution, excess thiophenol is removed by addition of Na2C03. The usual work-up gave the corresponding hydrocarbon in 84-100% yield and diphenylsulfide. The deuterated compounds are obtained if one uses C6H5SD and D20. 

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