Analysis of Heterocyclic Compounds

In this section we will demonstrate the applicability of the CS-NLC method for investigation of the effect of protonation on the symmetry of the molecules and the IR spectroscopic properties. In this respect, the CS-NLC method has also been successfully applied for the elucidation of organic dyes, in particular different dicy-anoisophorones, anyles, merocyanine dyes, and corresponding stilbazolium salts. 

A main point of emphasis of these investigations is the possibility of a comparison between the IR-LD spectroscopic data and those obtained by single-crystal XRD. 

FIGURE 4.1 Unit cells and hydrogen bonding of (a) bis(4-aminopyridinium) tetrachloropalladate(II), (b) 3,4-diaminopyridinium hydrodentartarate dihydrate, and (c) 3,4-diaminopyridinium hydrogensquarate. 

Stable dimers with an equally positioned proton between the anions. The geometry of the cation is flat with a maximal deviation from total planarity less than 0.2°. The obtained bond lengths and angles are typical, on comparing the values with the data for the four known salts of 4-cyanopyridine [253-255]. 

FIGURE 4.4 Nonpolarized IR (dashed line) and reduced IR-LD (solid line) spectra of 3,4-diaminopyridine after elimination of the band at 1670 cm . 

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See G.F. Riddell, "The Conformational Analysis of Heterocyclic Compounds", pags. 139-140, Academic Press, London, 1980. 

B-80MI20401 F. G. Ridell The Conformational Analysis of Heterocyclic Compounds ,... 

According to Stoddart (1), the unexpected preference for an electronegative substituent on C-l of a pyranoid ring to assume the axial orientation, first discussed by Edward (2) and later termed "the anomeric effect" by Lemieux (3), is now a generally recognized phenomenon in the conformational analysis of heterocyclic compounds. The preference for axial orientation is related to destabilization of the equatorial conformer in which a polar bond lies between two electron pairs on a vicinal oxygen atom. 

Stereochemistry of heterocyclic compounds . Parts 1 and 2, Armarego, W. L. F., Wiley-Interscience, New York, 1977 The conformational analysis of heterocyclic compounds , Riddell, F. G., Academic Press, 1980. 

In short, polarography can be used for the analysis of C—N, C—O, N—O, O—O, S—S, and C—S groups and for the analysis of heterocyclic compounds. Also, many important biochemical species are electroactive, such as vitamin C (ascorbic acid), fumaric acid, vitamin B factors (riboflavin, thiamine, niacin), antioxidants such as tocopherols (vitamin E), A-nitrosamines, ketose sugars (fructose and sorbose), and the steroid aldosterone. 

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