Phenanthrene description

In this chapter we will keep the description of transport simpler than Fick s law, which would eventually lead to partial differential equations and thus to rather complex models. Instead of allowing the concentration of a chemical to change continuously in space, we assume that the concentration distribution exhibits some coarse structure. As an extreme, but often sufficient, approximation we go back to the example of phenanthrene in a lake and ask whether it would be adequate to describe the mass balance of phenanthrene by using just the average concentration in the lake, a value calculated by dividing the total phenanthrene mass in the lake by the lake volume. If the measured concentration in the lake at any location or depth would not deviate too much from the mean (say, less than 20%), then it may be reasonable to replace the complex three-dimensional concentration distribution of phenanthrene (which would never be adequately known anyway) by just one value, the average lake concentration. In other words, in this approach we would describe the lake as a well-mixed reactor and could then use the fairly simple mathematical equations which we have introduced in Section 12.4 (see Fig 12.7). The model which results from such an approach is called a one-box model. 

In case the actual concentration of phenanthrene would exhibit significant spatial variations, the one-box model would not be the ideal description. Instead, it may be adequate to subdivide the lake into two or more boxes in such a way that within the defined subvolumes, phenanthrene concentration would be fairly homogeneous. So we would end up with a two- or multi-box model. In certain situations this box model approach may still not be sufficient. We may need a model which allows for a continuous concentration variation in time and in space. Such models will be discussed in Chapter 22. 

The Mono Lake (Sample 27) and South Pacific atoll (Sample 35) all show extremely high amounts of the phenanthrene series compared with the other PAH. We believe this variation is the result of other than experimental complications. Studies on Mono Lake sediments by Henderson et al. (17) indicate that algae are the predominant source for the organic content of the sediments. The same might be expected to be true of the atoll samples (see sample site descriptions). It is therefore possible that an alteration of the sterol content of the algae into phenan-... 

In Figure 29 we have illustrated the simplest shapes on a hexagonal map, those given by the periphery of benzene, naphthalene, anthracene, phenanthrene, phenalene, and pyrene. A simple way to represent the periphery of such objects parallels the description of a route on a dodecahedron outlined in the book by Rouse Ball and... 

Chapter 5 treats extension of the method to alkenes, alkynes and aromatic compounds by generalizing the force constant matrix. The relationship between bond orders and molecular geometry in conjugated systems is discussed along with VESCF inclusion in MM4. The valence bond description of molecular structure is discussed with special regard to MM4 results for phenanthrene, corranulene, and the C 60 fullerenes along with a general review of aromaticity and electronic spectra. 

In fact, it is endothermic by the not insignificant ca. 270 kJ/mol, belying that description. Pyrene is better understood as a polycyclic aromatic hydrocarbon. One may also consider pyrene as a biphenyl bridged by two ethylenes in the 2,2 - and 6,6 -positions or as a phenanthrene bridged by an ethylene in the 4,5-positions. If these were meaningful comparisons, we... 

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