Aromaticity conjugated circuit model

Several qualitative models, e.g. Platt s ring perimeter model [88], Clar s model [89] and Randic s conjugated circuits model [90-92] have either been or are frequently used for the rationalisation of their properties. All these qualitative models rationalise the properties of aromatic and anti-aromatic hydrocarbons in terms of the Hiickel [4n+2] and [4n] rules. The extra stability of a PAH, due to 7t-electron delocalisation, can also be determined, computationally or experimentally, by either considering homodesmotic relationships [36] or by the reaction enthalpy of the reaction of the PAH towards suitable chosen reference compounds [93],... 

Plavsic D, Nikolic S, Trinajstic N (1992) The Conjugated-Circuit Model - Application to Non—Alternant Hydrocarbons and a Comparison with Some Other Theoretical Models of Aromaticity. J Mol Struct (Theochem) 277 213... 

F. Zhang, X. Guo, and H. Zhang, Advances of Clar s aromatic sextet theory and Randic s conjugated circuit model. Open Org. Chem. J. (Suppl. 1-M6) (2006) 87-111. 

The conjugated-circuit model is a simple valence-bond resonance-theoretic model introduced for the study of aromaticity and conjugation of polycyclic conjugated systems which can be used to compute their r-resonance energies, RE. This model is a measure of the aromaticity in conjugated systems. Developed initially for polycyclic conjugated... 

The conjugated circuits model, as will be seen, offers insight into aromaticity that has been so far missing, and in that sense in our view it will be found... 

The chemistry of fullerenes appears to continue to grow steadily. The aromaticity of fullerenes has been reviewed in the recent issue of Chemical Reviews on aromaticity in an article by M. Buhl and A. Hirsch, entitled Spherical Aromaticity of Fullerenes . The title immediately sends a message of unsuspected novelty that has opened with the recognition of buckminsterfullerene s spherical structure, which as Kroto suggested could be the first example of a spherical aromatic molecule. We will only supplement this review by reporting on some aspects of fullerene aromaticity as described by the conjugated circuits model, as reflected in the works of Klein, Schmalz, and co-workers. They performed conjugated circuits calculations on all isomers of buck-minsterfullerene Geo, a total of 1812 isomers. The... 

In chemistiy, priority is to be given to experimental facts, not to calculations. Clar has offered experimental facts to support his model of the aromatic jr-sextet, but as we know, theoretical chemists have for the most part ignored his works. Recall the opening remark by R. G. Parr in this section. That is what has happened to Clar s aromatic jr-sextet. Now, with the synthesis of helical [/j]phenylenes by Vollhardt and co-workers, we may expect additional quantum chemical computations from theoretical circles. These are welcome. However, to fully appreciate the conjugated circuits model and the work of Clar, and to accept his model of the aromatic jr-sextet, apparently requires some imagination, or at least a... 

Interpretation of statistical and other data on molecules. In this article in particular we will see how graph theoretical concepts, such as the conjugated circuits, the innate degree of freedom of Kekule valence structures, and the Clar structures, can all be combined to characterize the local and overall aromaticity of benzenoid hydrocarbons, fully benzenoid hydrocarbons, and fully aromatic compounds. In addition, we will see that these approaches that lead to the quantification of Clar s r-sextets model can be justified using chemical arguments. ... 

Gutman and Cyvin have pointed out that the idea of symmetric difference known to mathematicians is closely related to conjugated circuits (vide infra). The questions of priority have always been painful and controversial in the sciences, as we have seen from the disputes over the invention of calculus between followers of Newton and Leibniz (see the biographical note on Cayley). Sometimes it is not even so important who first introduced a novel idea, but who developed the idea to a stage of maturation. For instance, the notion of the aromatic jr-sextet is originally attributed to Armitt and Robinson,but it was Clar who developed the model and deserves... 

We mentioned earlier the difficulty of the perimeter model, not only, as the case of corannulene illustrates, in that it gives wrong answers but also because it misleads one on believing that a large molecular periphery plays a critical role for determining aromatic and other molecular properties while the crucial role is played by smaller rings which can sustain conjugated circuits distribution. ... 

---