Quantitative approach to hückel rule the relations between the cycles of a molecular graph and the thermodynamic stability of a conjugated molecule

Cyclic Conjugation in Peropyrenes

“…The fact that the cycle C, = 1 + 2 has greater ef-value than the cycles C, = 2 + 3 and C, = 2 + 4 parallels the existence of Kekule structures in G-C, and the nonexistence of such structures in G -C, and G-C,, a well known [5] feature of cyclic conjugation. Another previously established [5] property of ef(G,C) is also confirmed by the data from According to the above formula the rings 1,4 and 7 would exhibit a pronounced local aromatic character. This prediction of the Clar theory 1251 is in agreement with the high ef-value (1032) of the peripheral rings 1 and 7, but in disharmony with the quite low ef-value (423) of the central ring 4.…”

“…Some ef-values of benzenoid hydrocarbons have been reported already in the first papers on the theory of cyclic conjugation [5,6,9], but their systematic study has been undertaken quite recently [lo,] I]. In [lo] benzenoid hydrocarbons with fixed single and fixed double bonds (i.e.…”

Local Aromaticity in Benzo- and Benzocyclobutadieno-Annelated Phenanthrenes

“…Taking into account the Sachs theorem [9,10], it is possible to express the energy effect ef (X) of a particular ring X, contained in the Benzocyclobutadieno-Annelated Phenanthrenes 341 molecular graph G, on the respective E value by Eq. (2) [11,12]:…”

Testing the Y–rule in Clar Theory

“…Details of the respective theory are outlined in the review (28) and elsewhere (29)(30)(31)(32)(33). For us it is important that positive e f -values imply thermodynamic stabilization due to cyclic conjugation.…”