Ring-energy content

Ring Energy Content of benzene rings in benzenoid hydrocarbons... 

Fig. 2. The Ring Energy Contents for particular benzene rings in tribenzopnenenthrapentaphene.

Ring energy content Ring energy content... 

Fig. 3a-b. Distribution of Ring Energy Content for benzenoid hydrocarbons and polysubstituted benzene derivatives. The interquartile ranges for the distribution are 25.9 kcal/mol and 16.1 kcal/mol,... 

Ring Energy Content in the ring of TCNQ moieties involved in Electron -Donor - Acceptor (EDA) complexes and salts... 

Fig. 4. Distribution of Ring Energy Content for TCNQ moieties in 106 EDA complexes and salts. The...

Ring Energy Content depending on the intermolecular H-bonding the case of p-nitrosophenolate anion... 

Ring Energy Content as a quantitative measure of fulfilling the Hiickel 4n+2 rule for derivatives of fuivene and heptafulvene... 

Fig. 7. Ring energy contents of fulvene, heptafiilvene and their derivatives.

Equation 16 provides an opportunity to calculate values of the energy content of a molecule or its fragment, referred solely to CC bonds. In this way, the ring energy content, REC, or the molecule energy content, MEC, are defined. 

The definition of aromaticity conceived by Hiickel strictly applies to monocyclic ring systems, but indole, constructed from the fusion of benzene and pyrrole, behaves as an aromatic compound, like quinoline and isoquinoline. The ring fusion, however, affects the properties of both components. This is reflected in the valence bond description of indole, shown in Scheme 7.1, where one canonical representation shows electron density shared between N-1 and C-3 in the pyrrole unit (implying enamine character). Note that although other canonical forms can be drawn, where the lone-pair electrons are delocalized into the benzenoid ring, their energy content is relatively high and they are of limited importance. 

Viewing photochromic systems on the basis of a 1,5-electrocyclization and its reverse, molecules must be envisaged in which the open ring as well as the cyclic structure have a similar energy content. This is the challenge in synthesizing molecules with tailor-made photochromic properties in connection with easy access to these molecules. 

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