Three-dimensional polynuclear aromatic

The aromatic hydrocarbons 1,2-7,8-dibenzocoronene (79) and 1,12-2,3-4,5-6,7-8,9-10,11-hexabenzocoronene (80) have been studied, using partial three-dimensional data, by Robertson and Trotter (1961a, b) as part of a series of investigations into polynuclear aromatic hydrocarbons. The carbon skeletons of dibenzocoronene and hexabenzo-coronene are planar to within 0-038 and 0-065 A respectively. The r.m.s. deviations of the atoms from the appropriate mean molecular planes are 0-016 and 0-024 A, compared with the average estimated standard deviations in atomic position of 0-012 and 0-020 A respectively. There are, however, some indications from the electron density maps... 

In classical structure-activity studies, most of the attempts concentrated on correlating the activity with one of the molecular properties— e.g., the carcinogenic activity of polynuclear aromatic compounds with their electronic structure (18, 19), the narcotic activity with lipophilicity 20, 21), the insecticidal activity of cyclodienes with their three-dimensional molecular silhouette 22), etc. Sometimes the activity correlated well with only one of the molecuar parameters. In our approach these are special cases where other physicochemical properties do not play critical roles in determining the variation in the activity within a set of congeners so that the coefficients defining these other properties are zero. 

This may be attributed to the pore structure of ZSM-5. Although the pores are large enough to allow the access or formation of aromatics up to Cio, the formation of polynuclear aromatics is probably severely constrained because ZSM-5 has no supercages like those in Y. Thus the selectivity for coke could be low. Moreover, as ZSM-5 has a three-dimensional channel structure the coke which is formed will cause the minimum loss of catalytic activity. 

The structures of organic polynuclear aromatic compounds are not limited to planar systems of carbon and hydrogen atoms. A classification of three-dimensional aromatic compounds is proposed on the basis of the number of recognizable edges (boundaries) in the molecular structure. Aromatic structures with no edges are included in this classification an example is the recently proposed truncated icosahedral structure for C6o (Buckminsterfullerene). The current literature and activity in the subfield of nonplanar aromatic compounds is reviewed. Three-dimensional aromatic compounds are possible tools for use in studies of polynuclear aromatic chemistry, and some possible applications to the particular chemical topics presented in this book are outlined. 

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. 

For some time, we have been interested in designing selective chemical modification reactions for coal with a particular emphasis upon characterizing the carbon skeleton of coal (2). The strategy for the approach starts with the working hypothesis that coal can be viewed as a three-dimensional macromolecule in which aromatic and hydroaromatic clusters are cross-linked to one another by various functional groups such as methylene units and polymethylene chains. In addition, the aromatic and hydroaromatic clusters, at least in bituminous coals, are assumed to be derived from polynuclear aromatic compounds (3, 4). 

Scheme I is a generalized scheme for the transformation of a polynuclear aromatic hydrocarbon to carbon and graphite. Heat treatment at about 350-500 °C leads to a complex reaction product mixture designated as pitch. Further reaction at temperatures near 500 °C results in an infusible polymeric hydrocarbon mixture designated as coke. As the heat-treatment process continues, the remaining hydrogen is removed, and a two-dimensional carbon polymer is formed. Finally, at temperatures near 3000 °C, three-dimensionally ordered graphite is produced.

Condensed polynuclear aromatic (COPNA) resins were used as precursor for carbonization by Kusakabe and co-woikers [64], Since COPNA resin is a thermoplastic resin with three-dimensional stmcture, the pore stracture of the carbonized COPNA membrane is expeeted to be different from that of the membrane fabricated by carbonization of PI which is hnear. COPNA corrrporrrrds were synthesized from polycyclic aromatic compormd (PCA) such as pyrene, phenanthrene and 1,4-ben-zenedimethanol (BDM) using p-toluene srriforrie acid as the eatalyst by the procedure given in Fig. 4.18. 

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