Steric effects in heteroaromatics, quantitative

Steric effects in heteroaromatics, quantitative analysis of, 43, 173 Substitution(s)... 

Gallo, R. J., Roussel, C., Berg, U., The Quantitative Analysis of Steric Effects in Heteroaromatics, 43, 173. 

Understanding, rationalizing, and predicting both reactivity and the energetics of dynamic stereochemistry are of major importance in heterocyclic chemistry and one or both of these topics are a concern of the majority of the contributions in Advances in Heterocyclic Chemistry. No previous systematic study has been reported which treats quantitatively steric effects in heteroaromatics this is the purpose of this article. 

The reason for writing this article is that important progress in the quantitative analysis of steric effects in heteroaromatics has been made recently by linear free energy relationships (LFER), geometrical, and theoretical methods. Also, heterocycles have been used to propose and exemplify new concepts and new parameters in physical organic chemistry. 

There has been a decisive evolution in the treatment of steric effects in heteroaromatic chemistry. The quantitative estimation of the role of steric strain in reactivity was first made mostly with the help of linear free energy relationships. This method remains easy and helpful, but the basic observation is that the description of a substituent by only one parameter, whatever its empirical or geometrical origin, will describe the total bulk of the substituent and not its conformationally dependent shape. A better knowledge of static and dynamic stereochemistry has helped greatly in understanding not only intramolecular but also intermolecular steric effects associated with rates and equilibria. Quantum and molecular mechanics calculations will certainly be used in the future to a greater extent. 

The longest chapter of this volume, authored by Roger Gallo and Christian Roussel (France) and Ulf Berg (Sweden), gives a comprehensive account of the quantitative treatment of steric effects in heteroaromatic compounds—a subject that has been advanced significantly by these authors. Finally, V. N. Charushin and O. N. Chupakhin (USSR) and H. C. van der Plas (The Netherlands) review reactions of azines with bifunctional nucleophiles. 

Quantitative analysis of steric effects in heteroaromatics, 43, 173 Quaternization... 

Quantitative study of steric effects in heteroaromatic compounds 88AHC(43)173. 

Heteroaromatic sulfoxides and sulfones ligand exchange and coupling in sulfuranes and //Avo-substitutions, 49, 1 Heteroaromatic systems, Claisen rearrangements in, 42, 203 Heteroaromatics, quantitative analysis of steric effects in, 43, 173 Heterocycles aromaticity of, 17, 255 chiral induction using, 45, 1 containing the sulfamide moiety,... 

The first important quantitative paper on steric effects in quaternization of heteroaromatics was by Brown and Cahn (55JA1715). The reaction rate constants for reaction of 2- 3-, and 4-monoalkylpyridines with methyl, ethyl, and isopropyl iodides, determined in nitrobenzene at several temperatures (Scheme 6), are summarized in Table II,... 

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