Polynuclear aromatic hydrocarbons general discussion

The theory and development of a solvent-extraction scheme for polynuclear aromatic hydrocarbons (PAHs) is described. The use of y-cyclodextrin (CDx) as an aqueous phase modifier makes this scheme unique since it allows for the extraction of PAHs from ether to the aqueous phase. Generally, the extraction of PAHS into water is not feasible due to the low solubility of these compounds in aqueous media. Water-soluble cyclodextrins, which act as hosts in the formation of inclusion complexes, promote this type of extraction by partitioning PAHs into the aqueous phase through the formation of complexes. The stereoselective nature of CDx inclusion-complex formation enhances the separation of different sized PAH molecules present in a mixture. For example, perylene is extracted into the aqueous phase from an organic phase anthracene-perylene mixture in the presence of CDx modifier. Extraction results for a variety of PAHs are presented, and the potential of this method for separation of more complex mixtures is discussed. 

Two general mechanisms are usually advanced to explain ionization of molecules in flames direct ionization by thermoionization, photoionization, or chemiionization and indirect ionization by charge transfer with other ions. The assessment of both mechanisms requires knowledge of the ionization potential of molecules. In the following discussion, computations developed in the Appendix are used to estimate approximate ionization potentials of polynuclear aromatic hydrocarbons. 

The various topics covered in this volume might seem to be more than sufficient. However, the aforementioned diversity of the general subject of polynuclear aromatic hydrocarbons has ensured that only a small fraction of the active areas of research on this topic can be discussed. I have therefore chosen as the main purpose of this introductory chapter to highlight an additional area of polynuclear aromatic hydrocarbon chemistry that is of recent personal interest, namely, nonplanar three-dimensional aromatic systems. The idiosyncracy of this choice is mitigated by significant recent discoveries in this subfield that are apropos to other chapters of this book. Therefore, at least part of the following discussion may be not only of interest but of practical use. 

The relation between polynuclear aromatic hydrocarbons and fossil fuels is discussed in introductory organic chemistry textbooks, which mention that coal and petroleum are the commercial sources of many aromatic hydrocarbons (5, 6). The chemistry discussed in these basic texts is generally limited... 

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