Overlap destructive

Fig. 9 illustrates that the two acetylenic systems become nearly parallel at C1-C6 distances close to 3 A where the constructive overlap of the re-orbital with one of the re -nodes is compensated by a destructive overlap with the other rc -node (Fig. 9, bottom). From a conceptual point of view, the properties of the in-plane re-system at the 3 A threshold bear a striking resemblance to the interaction of the two re-bonds in D2h cyclobutadiene where the re-re interaction is zero and the re-re repulsion is considerable, thus accounting for the extreme instability of this antiaromatic molecule.41 Even more relevant is a comparison with the TS of the symmetry forbidden thermal [2S + 2S] cycloaddition (Fig. 10) which prompted us to call this region antiaromatic .42... 

Figure 7.16 Real-time observation of the evolution of the t = 1, k = 0) state measured by the intensity of anti-Stokes scattering. The second excitation occurs 500ps after the first excitation. Only 4 fs shift of results in the change from constructive to destructive overlap. Reproduced with permission from Ref. [43]. Copyright 2013 by the American Physical Society.

Friedman and Krishnan, 1973b). As a result of overlap, some of the solvent co-sphere is displaced and if, for example, the effect of solute j on the solvent dominates the process of overlap, then the overlap can be represented as in Fig. 14(a), the change in the solvent being summarized by the reaction in Fig. 14(b). This mutually destructive overlap can be characterized by the free energy change, Aijt for the solvent reaction, where Ay is related to the thermodynamic energy, and entropy, by the expression A-, - — T. SSj. 

Draw the cr antibonding orbital that results from the destructive overlap of the two px orbitals just shown. 

This orbital results from the destructive overlap of lobes of the two p orbitals with opposite phases. If the signs are reversed on one of the orbitals, adding the two orbitals gives an antibonding orbital with a node separating the two nuclei ... 

The pi molecular orbitals of ethylene. The pi bonding orbital is formed by constmctive overlap of unhybridized p orbitals on the sp2 hybrid carbon atoms. Destructive overlap of thesep orbitals forms the antibonding pi orbital. Combination of two atomic orbitals must give exactly two molecular orbitals. 

If a cycloaddition produces an overlap of positive-phase orbitals with negative-phase orbitals (destructive overlap), antibonding interactions are generated. Antibonding interactions raise the activation energy, so the reaction is classified as symmetry-forbidden. The thermal [2 + 2] cycloaddition of two ethylenes to give cyclobutane is a symmetry-forbidden reaction. 

An overlap of orbitals that contributes to antibonding. Overlap of lobes with opposite phases (+ phase with — phase) is generally destructive overlap, (p. 671)... 

Figure 3 XAS spectrum with absorption maxima (Ej) and minima (E2) in the EXAFS. Inset constructive and destructive overlap of photoelectron wave...

A third factor is the symmetry of the orbitals—two AOs must have the appropriate symmetry to combine. Thus a 2p orbital cannot combine with a 2py or 2p orbital since they are all perpendicular to each other (they are orthogonal). Depending on the alignment, there is either no overlap at all or any constructive overlap is cancelled out by equal amounts of destructive overlap. Likewise, an s orbital can overlap with a p orbital only end-on. Sideways overlap leads to equal amounts of bonding and antibonding interactions and no overall gain in energy. 

Figure 2.6 Hydrophobic interactions. Cartoon of the destructive overlap of two hydrophobic hydration shells (striped areas) resulting in a release of water to the bulk solution.

The side-by-side overlap of two 2p orbitals in ethene leads to two molecular orbitals. Constructive overlap gives the bonding n, molecular orbital. The destructive overlap of the two orbitals gives a higher energy, antibonding molecular orbital, ti. ... 

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