Polycyclic benzenoid hydrocarbons

CONTENTS List of Contributors. Introduction to the Series An Editor s Forward, Albert Padwa. Preface, Randolph P. Thummel. Cyclooctatetraenes Conformational and ii-Elec-tronic Dynamics Within Polyolefinic [8] Annulene Frameworks, Leo A. Paquette. A Compilation and Analysis of Structural Data of Distorted Bridgehead Olefins and Amides, Timothy G. Lease and Kenneth J. Shea. Nonplanarity and Aromaticity in Polycyclic Benzenoid Hydrocarbons, William C. Herndon and Paul C. Nowak. The Dewar Furan Story, Ronald N. Warrener. Author Index. Subject Index. 

Two or more benzene rings fused together form a number of polycyclic benzenoid aromatic compounds, naphthalene, anthracene and phenanthrene, and their derivatives. All these hydrocarbons are obtained from coal tar. Naphthalene is the most abundant (5%) of all constituents of coal tar. 

Polansky and Derflinger proposed a useful concept of benzene character which is the projection of the ocupied it-MO s in a given hexagon L of a polycyclic benzenoid hydrocarbon onto the three occupied MO s of a benzene molecule located on that position [27]. This quantity is shown to be expressed as a linear combination of the Coulson bond order for the component six bonds and for the three para-bonds in L. Their original definition of the benzene character for L can be transformed into the normalized benzene character as [28]... 

Balaban and Artemi wrote very recently (1990) [63]. The enumeration of polycyclic benzenoid hydrocarbons (polyhexes, or benzenoids) continues to be a challenging problem. The field has been flourishing, not least during the very last few years, as documented by the present list of references. It contains 16 relevant publications from 1989, which can be supplemented by a few more... 

In their analysis of the topological dependency of the aromatic sextet in polycyclic benzenoid hydrocarbons Ohkami and Hosoya [37] arbitrarily define two types of ring perfect matchings viz , orooet and improper as shown below ... 

E C omaticity in Polycyclic Benzenoid Hydrocarbons, William C. Herndon and Paul C. Nowak. The Dewar Furan Story, Ronald N. Warrener. Author Index. Subject Index. Volume 3,1995, 316 pp. 97.50 ISBN 1-55938-698-3... 

Herndon, W.C. and Szentpaly, L.V. (1986) Theoretical model of activation of carcinogenic polycyclic benzenoid aromatic hydrocarbons. Possible new classes of carcinogenic aromatic hydrocarbons. 

Members of a class of arenes called polycyclic benzenoid aromatic hydrocarbons possess substantial resonance energies because each is a collection of benzene rings fused together. 

A large number of polycyclic benzenoid aromatic hydrocarbons are known. Many have been synthesized in the laboratory, and several of the others are products of combustion. Benzo[a]pyrene, for example, is present in tobacco smoke, contaminates food cooked on barbecue grills, and collects in the soot of chimneys. Benzo[a]pyrene is a carcinogen (a cancer-causing substance). It is converted in the liver to an epoxy diol that can induce mutations leading to the uncontrolled growth of certain cells. 

Polycyclic benzenoid hydrocarbons are compounds that contain two or more fused benzene rings. Fused rings share two adjacent carbons—naphthalene has two fused rings, anthracene and phenanthrene have three fused rings, and tetracene, triphenyl-ene, pyrene, and chrysene have four fused rings. There are many polycyclic benzenoid hydrocarbons with more than four fused rings. 

Like benzene, all the larger polycyclic benzenoid hydrocarbons undergo electrophilic substitution reactions. Some of these compounds are well-known carcinogens. The chemical reactions responsible for causing cancer and how you can predict which compounds are carcinogenic were discussed in Section 12.8. 

Polycyclic benzenoid hydrocarbons contain two or more fused benzene rings fused rings share two adjacent carbons. Polycychc benzenoid hydrocarbons undergo electrophilic aromatic substitution reactions. Naphthalene undergoes irreversible substitution predominantly at the 1-position and reversible substitution predominantly at the 2-position. The nature of the substituent determines which ring of a substi-tuted-naphthalene undergoes electrophilic substitution. 

Of the numerous aromatic polycyclic benzenoid hydrocarbons discussed by Kry-gowski and Cyranski in their chapter [50], there are enthalpy-of-formatibn data for fewer than half of them. Despite the paucity of compounds for which there are data, there is no scarcity of data itself for naphthalene alone there are at least 10 determinations of the enthalpy of formation of the solid and 15 of its enthalpy of sublimation All but a few of the solid substances have more than one reference for an enthalpy of formation and usually several references for the enthalpy of sublimation. Benzene, a liquid, seems the sole compound for which there are relatively few measurements and consistent results. Our favorite compendium of data [4] does not include some of the more recent values so we begin by recommending gaseous... 

Condensed polycyclic benzenoid aromatic hydrocarbons are customarily regarded as planar molecular structures because of the geometrical constraints of carbon atoms in a state of sp2 hybridization. A well-known exception is the class of compounds called the helicenes (18) for which the nonbonded overlap of two terminal benzenoid rings in a cata-condensed structure, as in structure 1, forces a molecule into a nonplanar helical structure. A second exceptional class of compounds is related to corannulene (2) and other an-nulenes of this type (19, 20). In corannulene, strain associated with the pericondensed five- and six-membered rings requires adoption of a bowlshaped structure (20, 21). For both structures 1 and 2 the aromatic character of the benzenoid rings is retained to an appreciable extent. 

Theoretical methods to predict chemical reactivity properties of polycyclic benzenoid aromatic hydrocarbons are reviewed. These methods include the usual molecular orbital (MO) quantum chemical calculations, as well as pencil-and-paper MO and valence-bond procedures to derive indexes related to the rates of chemical reactions. Justification for the pencil-and-paper procedure termed the pertur-bational molecular orbitahfree-electron method (PMO F) is presented, and the modifications (PMO.Fw) of this procedure necessary to handle the differing reactivity patterns with neutral and ionic intermediates are also given. Examples of correlations of experimental results are used to illustrate these modifications. 

The QUANTUM theoretical characterization of the molecular structure of polycyclic benzenoid aromatic hydrocarbons (PAHs) and the relationships of structure to the physical and chemical properties of PAHs are problems that have been of concern to theoreticians (and experimentalists) for more than 50 years. In general, quantum chemical procedures can be used successfully to correlate kinetic and thermodynamic data for PAHs. These procedures are usually restricted to the it systems of the PAHs and normally seem to yield very good results because (1) the it system properties are described accurately by quantum mechanical calculations and (2) the energetics of a given type of reaction in a group of related PAHs is mainly... 

These ideas were applied for comparing aliphatic alcohols, carcinogenic polycyclic benzenoid aromatic hydrocarbons, and binding constants between human corticosteroid binding globulin and a set of 47 steroids. The last set of compounds was also investigated by comparative molecular field analysis (CoMFA) with comparable results. A similar approach was used by Klopman and Raychaudhury on the basis of the Wiswesser Line Notation system. 

Polycyclic benzenoid hydrocarbon An extended rr.sy.stcm of I li.scd rings, al.so called a polycyclic aromatic hydrocarbon (PAH). 

Naphthalene Two fused benzene rings, the simplest polycyclic benzenoid hydrocarbon. 

In 1997, Bird studied the absolute hardness as a criterion for heteroaromaticity. In this study, it was found that good correlations existed between the Zhou and Parr hardness values and the REPE values for polycyclic benzenoid hydrocarbons but that the correlation was not good when heterocyclic compounds were included. This was also confirmed in a 1998 study by Bean, where only a very low correlation between the HOMO—LUMO gap, on one hand, and geometric, energetic, and other delocalization measures was found for a series of five-membered heteroaromatic compounds. However, Bird suggested using the reformulation of the hardness in terms of molar refractivity as suggested in the work of Komorowski ... 

Herndon WC (1990) On Enumeration and Classification of Condensed Polycyclic Benzenoid Aromatic Hydrocarbons. J Am Chem Soc 112 4546... 

A large number of polycyclic benzenoid aromatic hydrocarbons are known. One of these, benz[tobacco smoke. From the literature, locate and then draw the structure of this hydrocarbon. Can you suggest other sources where this material might be expected to be present ... 

A. T. Balaban and M. Randic, Partitioning of jc-electrons in rings of polycyclic conjugated hydrocarbons Part 6. Comparison with other methods for estimating the local aromaticity of rings in polycyclic benzenoids, J. Math. Chem. 37 (2005) 443-453. 

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