Resonance energy topological

The concept of relative hardness and topological resonance energy per electron as a measure of aromaticity, with a relative hardness value of zero as the border for antiaromaticity, failed for 1-benzothiepin,3 2... 

Topological Resonance Energies (TRE), Hess-Schaad Resonance Energies (HSRE), and Ring Current Indices (RCI) ... 

Topological resonance energy studies of the three isomeric thienopyrimidines show that while all of the ring systems are aromatic, the thieno[3,4-, pyrimidine class of compounds is less aromatic by approximately 20%. Correspondingly this system is believed to be considerably more reactive than its isomers <1997CCA841>. 

Theoretically derived resonance energies (RE) (70T4269), resonance energies per ir-electron (REPE) (72T3657) and topological resonance energies (TRE) (77JA1692) are listed... 

Topological resonance energy (TRE) values suggest that 346 is considerably less stable than 345. CNDO/2 calculations with inclusion of d-orbital participation for 346 show considerable 7i-bonding between carbon and sulfur of which over half is attributable to pTt-dn overlap the degree of charge separation indicates that canonical resonance forms of type b (carbonyl ylide type) are more important than those of type c (thiocarbonyl ylide type)." ... 

Results of MNDO calculation of lA-azonine (35 X=NH) are in agreement with experimental evidence that this is a planar, aromatic molecule. The calculated geometry of oxonin (35 X = 0), as a buckled, unsymmetrical polyenic heterocycle, is also in agreement with its known properties. The MNDO calculations on thionin (35 X = S) indicate that this molecule is planar, which should allow effective tt delocalization, and at least some aromatic character (86MI927-OI). The topological resonance energy model also predicts lA-azonine and thionin to be aromatic, and oxonin nonaromatic (84JHC273). 

TRE(PE) topological resonance energy per electron. The values are expressed as percentages of the value for benzene. 

The stability of BHs (and conjugated systems in general) is usually appraised through the topological resonance energy per electron, TRE(PE), [31]. Unfortunately, though we cannot deny that the concept of TRE has a certain elegance and simplicity, there are numerous examples of the stability predictions based on TRE that are contrary to the chemical sense. In particular, molecules with unpaired electrons (radicals) are predicted to be excessively stable within the TRE approach [32]. 

The degree of 7t-electron stabilization exhibited within the A,B-diheteropentalenes is dependent on the relative orientation of the two heteroatoms [64,65], Topological resonance energy values [64] and heats of formation from MNDO calculations [65]... 

A theoretical investigation of [njcydophenacenes was reported by Aihara, who discussed stability of [njcyclophenacenes with a topological resonance energy (TRE) method [10] and proposed that the cydophenacenes are aromatic and stable... 

The abbreviation TRE comes from topological resonance energy , as this measure of the overall cyclic conjugation in a polycyclic conjugated molecule was originally named [35,44], The TRE-concept was introduced in 1976 independently by Aihara [34] and by Milun, Trinajstic and the present author [35, 44, 45], Aromatic conjugated molecules have positive whereas antiaromatic molecules have negative TRE-values. 

Kurihara T, Motohashi N, Gui-Lin Pang, Higano M, Kiguchi K, Molnar J (1996) Correlation between topological resonance energy of methyl-substituted Benz[c] acridines, Benzo [a] phenothiazines and Chrysenes, and their carcinogenic or antitumor ac-tivites. Anti cancer Res 16 2757-2766... 

The main difficulty with the RE concept is the hypothetical nature of the reference structure, its choice being somewhat arbitrary. There are many ways of defining RE (M. Dewar, C. F. Wilcox, and others). Here we shall briefly examine the topological resonance energy (TRE). TRE is a nonparametric index which is directly related to the topology of a molecule and is of great practical value in predicting the aromatic stability of an arbitrary jt-network. 

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