Electron resonance energy per

Benzene rings can also be fused in angular fashion, as in phenanthrene, chrysene, and picene. These compounds, while reactive toward additions in the center ring, retain most of the resonance energy per electron (REPE) stabilization of benzene and naphthalene. ... 

Table 5. Resonance Energy and Resonance Energy per Electron of (Benzo)Thiepins8...

HMO calculations have been ultilized in the search for substituted thiepins liable to be good candidates for synthesis due to electronic substituent effects.7 Based on these results, the presence of at least two carboxy groups and one fluorine group give an increased resonance energy per electron to positive values, indicating at least some thermal stability. 

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... 

As A. and B. Pullman showed more than 40 years ago, the purine base adenine occupies a unique situation in the purine family in comparison to the other purines, it has the greatest resonance energy per -electron, i.e., it is more stable, and thus likely to have been incorporated preferentially into biomolecules (Pullman, 1972). 

The HMO resonance energy per electron (REPE value5,48) using an appropriate reference structure was found to be 0.040 / (cf. pyrrole 0.039 / , indolizine 0.027 /3).s... 

Resonance Energy per Electron (REPE Values5) of CyclI3,3,3)azines°... 

HMO calculations, based on localized polyenes instead of isolated alkenes, can account for the heats of atomization of furan (41.64 observed, 41.69 eV) and of dibenzofuran (109.09 observed, 108.92 eV). For resonance energies (quoted as resonance energy per electron, REPE) they give furan, 0.007 oxepin, -0.006 benzo[6]furan, 0.036 benzo[c]furan, 0.002 and dibenzofuran, 0.047 /3 (72T3657). That furan emerges as hardly more aromatic than a diene while pyrrole (REPE 0.039/3) is clearly aromatic is in line with other results, including those from MINDO/3 and topological methods (see Section... 

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]. 

Table 1 lists some calculated resonance energies per electron (in ft units) for thienothiophenes, pentalene, and pentalene dianion <72T3657, 75T295, 77JA1692). These data support the conclusions of Gimarc s proposition. 

The resonance energy per electron for the sulfur-containing heterocycles (13)-(15) (X = Y = S) have been determined. The values are —0.005/1, —0.008/1, and — 0.012/S, respectively. These values, when compared with thiophene (0.032/1), indicate these isomers (13)-(15) are not aromatic (73JA3907). 

The resonance energy per electron (REPE) is a size-independent quantity obtained by dividing the total resonance energy for the number of n -electrons. 

Lukovits149 calculated the resonance energy per electron (REPE) of graphite sheets using the expression that he obtained from equations (11), (55), (58), (60) and (61) ... 

The Number of Conjugated Circuits in Nanotubes. Lukovits and Janezic182 calculated the number of conjugated circuits in armchair (1,1 ) carbon nanotubes and ( , )i nanoribbons and used them to obtain the resonance energies per electron (REPE) of these structures. For any (1,1) , nanotube, they derived the following formulae for 6- and 10-membered circuits in terms of the corresponding Kekule structures ... 

There is another way to test chemical stability hat can be applied to aromatic organic compounds. Aromaticity is usually taken to mean high stability and low reactivity. It can be quantified by calculating the resonance energy per electron (REPE). These values are usually calculated by simple Huckel theory, but they correlate well with experimental measures of reactivity. ... 

For organic solids the individual molecular properties are used. For explosives containing aromatic rings, there is a correlation between the sensitivity and the resonance energy. The smaller the resonance energy per electron (REPE), the more sensitive is the compound. All these examples show the expected relationship the softer the solid (in chemical terms), the more reactive it is. 

Molar refractivity is easily derived from the refractive index. Hardness measured in this way correlates with other aromaticity criteria such as resonance energy per electron for a variety of hydrocarbons and heterocyclic molecules (see p. 141) ... 

Two other semiregular nets examined in 1968 [1] and 1994 [8 were [3, 9 and (4, 6, 12 with resonance energies per electron -0.007 and -0.0744 eV, respectively. Other 3-connected planar nets, but without regular polygons, were analyzed. From... 

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