Benzene rings angular fusion

Polynuclear aromatic hydrocarbons formed by the angular fusion of benzene rings may adopt either planar or nOnplanar minimum energy conformations, as demonstrated by the circulenes 8-10. [6]Circulene (coronene 9), the earliest known member of the family, prefers a planar structure of symmetry since the presence... 

The structures of the compounds were verified by H NMR spectroscopy. Two doublets of benzene ring protons (7 = 9 Hz) characteristic of mutual ott, ti-positions indicated angularly ring-fused structures. The shifts of NMR peaks and the features of the IR spectra (containing deformed out-of-plane vibrations at 800 cm ) were characteristic of 1,2,3,4-tetrasubstitution and so also confirmed the angular ring fusion. 

Peri fusion Angular fusion of benzenes, as in the three-ring system phcmin-Ihrcne. 

Naphthalene, anthracene, and phenanthrene are the three simplest members of this class. They are all present in coal tar, a mixture of organic substances formed by heating coal at about 1000°C in the absence of air. Naphthalene is bicyclic and its two benzene rings share a common side. Anthracene and phenanthrene are both tricyclic aromatic hydrocarbons. Anthracene has three rings fused in a linear fashion an angular fusion characterizes phenanthrene. The structural formulas of naphthalene, anthracene, and phenanthrene are shown along with the numbering system used to name their substituted derivatives ... 

Continued angular fusion of benzene rings to phenanthrene eventually results in helical polycyclic benzenoid arrays, called helicenes. These molecules are chiral and, when they are optically pure, exhibit extraordinary specific rotations—for example, for the helicene shown,... 

Polycylic aromatic hydrocarbons with both angular and linear types of ring fusion show absorption curves of a similar profile to that of benzene but with the absorption maxima shifted to longer wavelengths the greater the number of rings the more pronounced the shift. 

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