A resonance energy

Most MO methods find a bond alternation pattern in the minimum-energy structure, but calculations that include electron correlation lead to a delocalized minimum-energy structure. Thus, although the n system in 1 is not completely planar, it appears to be sufficiently close to provide a delocalized 10-electron Ji system. A resonance energy of 17.2 kcal has been obtained on the basis of an experimental heat of hydrogenation. ... 

C O , that is, the normal covalent carbon-oxygen double bond,- the estimated bond energy 6.60 v.e., then the ketones would show a resonance energy of 1.11 v.e. arising from the + —... 

Pyrrole, C4H6N, is found to have a resonance energy of 0.98 v.e., despite the fact that the structure... 

A corresponding correlation is obtained for the rate constants of a,a -phenyl substituted alkanes 26 (R1 = C6H5, R2 = H, R3 = alkyl) (see Fig. 1 )41). It has, however, a different slope and a different axis intercept. When both correlations are extrapolated to ESp = 0, a difference of about 16 kcal/mol in AG is found. This value is not unexpected because in the decomposition of a,a -phenyl substituted ethanes (Table 5, no. 22—27) resonance stabilized secondary benzyl radicals are formed. From Fig. 1 therefore a resonance energy of about 8 kcal/mol for a secondary benzyl radical is deduced. This is of the expected order of magnitude54. ... 

Huang XY, Li L, Qian HF, Dong CQ, Ren CJ (2006). A resonance energy transfer between chemiluminescent donors and luminescent quantum-dots as acceptors (CRET). Angew. Chem. Int. Ed. 45 5140-5143. 

F ure 5.19 The energy-level schemes of donor D and acceptor A centers for (a) resonant energy transfer and (b) phonon-assisted energy transfer. 

First, the range of separation. The experimentally determined tip-sample separation is 1-4 A before a mechanical contact (Diirig et al. 1988). For most metals, the normal nucleus-nucleus distance of a mechanical contact is 2.5-3 A. Therefore, on the absolute tip-sample scale, it is 3.5-7 A. By comparing with the case of H2, we notice that this is the range where the resonance interaction dominates. In other words, under normal STM operation conditions, over a distance range of about 3 A, resonance energy is almost solely responsible to the atomic force, and the distance dependence of the force should be approximately exponential. 

The chemistry of cyclazines has not previously been reviewed. It is our aim to survey the methods of synthesis of these compounds and to show that the chemistry of cyclazines has stimulated discussion on theories of condensed -systems. This latter point may be illustrated by an example Early molecular orbital (MO) studies on cycl[3,3,3]azine (2) predicted a resonance energy greater than that for the highly stable... 

These differences in magnitudes and even sequences of estimated resonance energies are symptomatic of the difficulties involved in defining quantitatively what constitutes a resonance energy. Regardless of these problems, in terms of general characteristics, i.e. spectroscopy (see Section 3.13.3) and reactions, thiophenes with only rare exceptions exhibit... 

The early evaluations of DE (Section 2.26.2.1) for 1,4-dithiin and thianthrene, which suggested that both ring systems have aromatic character, received support from an empirical measurement of the resonance energy of thianthrene using combustion methods. The compound was found to have a resonance energy of 71 kJ mol-1 in excess of that for two benzene rings (55ACS847). However, it will be recalled that more recent theoretical treatments... 

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