Positive overlap

In all three frontier orbital combinations shown above, the upper orbital components are the same sign, and their overlap is positive. In the two cases on the left, the lower orbital components also lead to positive overlap. Thus, the upper and lower interactions reinforce, and the total frontier orbital interaction is non-zero. Electron movement (chemical reaction) can occur. The right-most case is different. Here the lower orbital components lead to negative overlap (the orbitals have opposite signs at the interacting sites), and the total overlap is zero. No electron movement and no chemical reaction can occur in this case. 

The construction of the acc molecular orbitals is solved in exactly the same manner each acc bond orbital has a positive overlap with its two neighbors via this overlap, the bond orbitals mix and form three typical combinations (see Fig. 25). A glance at... 

A positive overlap between the orbitals gives rise to the bonding orbitals while lack of overlap forms antibonding orbitals. 

H2-----H2 interaction repulsive. The net result is a positive overlap population... 

The last condition, the orientation principle, is illustrated for the benzene-iodine and ethylene-platinum complexes. It is seen that the orientation depicted in Fig. 2a leads to a positive overlap integral and... 

Scheme 1.5 represents case f, that is, an anion-radical belonging to the borderline between moderately and completely delocalized species. Its optical spectra, along with frontier orbital analysis, testifies that in this anion-radical there is a positive overlap between C-N bonds and the psendo-geminal carbons of the opposite rings, as shown by the dashed lines in the strnctnre of Scheme 1.5 (Nelsen et al. 2005). Taken together, the experimental results considered provide direct evidence for the throngh-bond mechanism of electron transfer in these paracyclophane systems.

To determine which of the two roots is lower in energy, one needs to know whether the wave functions of A and suffer constructive interference (positive overlap) or destructive interference (negative overlap). Let us assume that the wave functions are in phase (positive overlap). Then hAB will be negative since / (1) is negative, and the upper and lower roots, u and l, respectively, are... 

Figure 8.3 By combining the central s orbital with the ligand orbital SALC to give either positive overlap or negative overlap, we get i//h and respectively. The expressions written for these are only meant to express this sign relationship the actual expressions for (/a and if/h contain different coefficients.

When these two sets of Tu orbitals are combined with positive overlap (as... 

In order to actually participate in a u bond within the complex, a metal orbital must be capable of positive overlap with a ligand group orbital directed along the bonding axes. For the moment, let us merely consider the directional requirement and... 

Fig. 11.17 Overlap of ligand orbitals in the rv plane with metal (a) and ilty (b) orbitals. Note that an appropriate choice of sign for the ligand orbitals provides positive overlap with the dxi.ys orbital, however, no single sign choice for the ligand wave function produces positive overlap with the d orbital...

Rg. 16.58 Multiple bonding between rhenium atoms (a) Formation of a r bond from overlip of iH orbital of cadi rhenium atom, (b) Formation of a n bond from overlap of the orbital of each rhenium alum. A second c bond forms m Ihe yz plane, (c) Positive overlap from d.r orbitals to Form t> ft bond in ihe eclipsed conloimitmn staggered conformation. [In part from Cotton. F A. Aiv. Client. Res. 1969. 2. 240. Reproduced with permission.]... 

Depending on the relative symmetry of the p orbitals, a bonding (that is, a positive overlap) is obtained either for the conrotatory or for the disrotatory motion, and these result in different stereochemistries if the terminal atoms carry distinct substituents, as shown in Figure 4.41(b). 

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