Heteroaromatics, quantitative analysis

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,... 

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

In the context of the stability of the nitrosoamine intermediate in the diazotization of heteroaromatic amines relative to that in the case of aromatic amines, the reversibility of diazotization has to be considered. To the best of our knowledge the reverse reaction of a diazotization of an aromatic amine has never been observed in acidic solutions. This fact is the basis of the well-known method for the quantitative analysis of aromatic amines by titration with a calibrated solution of sodium nitrite (see Sec. 3.3). With heteroaromatic amines, however, it has been reported several times that, when using amine and sodium nitrite in the stoichiometric ratio 1 1, after completion of the reaction nitrous acid can still be detected with Kl-starch paper,... 

Electrochemical induction of the reaction (Pinson and Saveant, 1974), as shown to occur in a number of cases with aromatic and heteroaromatic substrates (Saveant, 1980a, 1986, 1988), also provides evidence for the Sr I mechanism. The electrochemical approach allows, in addition, a quantitative analysis of the mechanism and reactivity problems and will be described in this connection in the next subsection. 

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

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. 

In Section II, devoted to intermolecular processes, it appeared that most of the quantitative analysis of steric effects was made using a single parameter approach. However, analysis has shown that a correct description of the size of a substituent rests on its preferred conformational states, which are related to the interactions with both the planar heteroaromatic ring to which it is bonded and neighboring groups. This was the topic of Section III. 

Qualitative Analysis. High-resolution MS generally can separate and identify the formulas of essentially all heteroaromatic components containing one or more oxygen, sulfur, and nitrogen atoms per molecule, although some difficulties remain in the routine identification of sulfur compounds. The approach used to compensate for the latter difficulty is discussed in the section on quantitative analysis. 

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

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