Charge resonance

Figure 2-52. a) Two semipolar resonance structures are needed in a correct VB representation of the nitro group, b) Representation of a nitro group by a structure having a pentavalent nitrogen atom, c) The RAMSES notation of a nitro group needs no charged resonance structures. One jr-system contains four electrons on three atoms. 

The 1,3-dipolar cycloaddition reactions to unsaturated carbon-carbon bonds have been known for quite some time and have become an important part of strategies for organic synthesis of many compounds (Smith and March, 2007). The 1,3-dipolar compounds that participate in this reaction include many of those that can be drawn having charged resonance hybrid structures, such as azides, diazoalkanes, nitriles, azomethine ylides, and aziridines, among others. The heterocyclic ring structures formed as the result of this reaction typically are triazoline, triazole, or pyrrolidine derivatives. In all cases, the product is a 5-membered heterocycle that contains components of both reactants and occurs with a reduction in the total bond unsaturation. In addition, this type of cycloaddition reaction can be done using carbon-carbon double bonds or triple bonds (alkynes). 

The asymmetric dissociation channels discussed in the previous section are closely tied to the charge-resonant states first introduced by Muliken in 1939 [35]. These states have no counterpart in atoms and occur whenever there is a difference in charge state in the dissociation limit of a diatomic molecule. They... 

Fig. 1.11. Ground state and excited charge resonant states of a model doubly-charged diatomic molecule. The electronic configurations of the states are shown schematically in a 1-D double-well potential...

Charge density wave, 54 Charge spreading, 127 Charge-resonant states, 13, 18 Charge-asymmetric dissociation, 9 Coherent control, 7... 

Hydroxytriphenylmethane derivatives give rise to anionic charge-resonance systems that are isoconjugate with the corresponding amino-substituted dyes. Thus, for example, the oxonol analogue of malachite green is benzaurine (Scheme 6.33). The quinonoid neutral form (6.184), which is pale yellow, produces a violet anion (6.185) on the addition of alkali in... 

Fluorescein (6.198 X = H Cl Acid Yellow 73) is the xanthene analogue of phenolphthalein (6.190) and gives rise to an anionic charge-resonance system. This was the... 

The first cyanine dye was made in 1856 by Greville Williams. Thus the blue charge-resonance system 6.216 was produced when oxidative coupling took place between N-... 

We note at this point that, when the two fragments become identical, the charge transfer configurations and the locally excited configurations will have to be replaced by charge-resonance and exciton-resonance configurations, respectively. 

Fig. 55. Configuration interaction diagram for (a) 1,1 difluoroethane and (b) 1,2 difluoroethane. nj and ft2 are charge resonance configurations, i.e.

To obtain a more penetrating view on A as an interaction between the original single wells, we compare two analytical routes to the evaluation of the basic two-center charge resonance integrals in this limit WKB and the lowdimensional perturbation formula. 

It is a characteristic of all these conjugate acids that the positive charge is distributed over the whole molecule by a charge resonance. 

To the best of our knowledge, pulse radiolysis transient absorption studies of neat CS2 have not been reported. CS2 anion in 0.1 M cyclohexane and 0.1 M THF solutions appears as a single 275-nm peak [35] there is no charge-resonance band that can be attributed to the dimer anion, at early (< 10 nsec) or later times. 

Cycloreversion of TPCB" and dimerization of St are summarized in Scheme 3, in which TT-(t-St)2, cr-St2, and the t-St /t-St pair are involved as the key intermediates. ir-(t-St)2 takes various overlapping arrangements of the rr-electrons between two benzene rings, and exhibits a large charge resonance (CR) band at shorter X of 680-800 nm than those of other dimer reported [84], On the other hand, a-St 2 has an acyclic linear structure. 

The third radical cation structure type is the cyclohexane-1,4-diyl radical cation (22 +) derived from 1,5-hexadiene. The free electron spin is shared between two carbons, which may explain the blue color of the species ( charge resonance). Four axial p and two a protons are strongly coupled (a = 1.19 mT, 6H). + ... 

Fig. 11. Energy diagram illustrating origin and configuration interaction of lowes exciton and charge resonance states of point group AC-...

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