Organic acids structural description

This chapter examines the fundamental structural properties of organic molecules that directly or indirectly affect pKa values of organic acids, making it possible to estimate theoretical upper limits for concentrations of common acidic functional groups, to assess methods of quantitative analysis of acidic functional groups in humic substances, and to examine several models that have been proposed for the description of proton binding by humic substances. Some of the concepts that appear obvious in the context of this chapter have been included for the simple reason that the literature on acidity of humic substances reveals that these points have frequently been either misunderstood or neglected. 

A useful way to organize these biosynthetic pathways is to group them into six families corresponding to their metabolic precursors (Table 22-1), and we use this approach to structure the detailed descriptions that follow. In addition to these six precursors, there is a notable intermediate in several pathways of amino acid and nucleotide synthesis—5-phosphoribosyl-l-pyrophosphate (PRPP) ... 

Regioselective synthesis is examined mainly on the basis of the conception of competitive coordination and the principle of hard and soft acids and bases [14]. A description of polyhedron-programmed synthesis is given, taking into consideration thin structure compounds to be used as ligands (number, nature, and mutual situation of donor centers and the presence and character of organic fragments, annealed to a metal-cycle). 

The detailed chemical structures of the organic components of soil and sediments are largely unknown, and terms such as humic acid and fulvic acid are primarily descriptive rather than representing chemically defined entities. A brief summary is given of studies aimed at providing information on the structural components of humic and fulvic acids. Further studies using specific chemical reactions are given below. 

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