Bond-distorted orbital

Shaik, S. Hiberty, P. C. Shurki, A. Wu, W. Danovich, D. Unpublished VB calculations on 3-electron—3-center, 4-electron— 4-center, and 6-electron—6-center species. These VB calculations which are cited in this study were performed at the VBSCF/6-31G level. A bond in a localized structure is expressed with bond-distorted orbitals as explained by Mo et al.149... 

In a more restrictive definition of the CF orbitals, each orbital is allowed to delocalize only onto the atom to which it is bonded in the VB structure under consideration such orbitals are called bond-distorted orbitals (BDOs). 

BDO Bond distorted orbital. An orbital that is localized on one atom with a small delocalization tail on an atom with which it shares a bond. 

Structures considered are quinolizinium (187), and 1,5- (188), 1,6- (189), 1,7- (190), 1,8- (191), and 2,7- (192) naphthyridines. In the naphthyridines the 10 7r-electrons are delocalized in five bonding molecular orbitals, which are distorted by the annular nitrogens in such a way that positions ortho and para to those nitrogens are less likely to be electrophilically haloge-nated than meta carbons. Compounds with a nitrogen at the ring junction carry a positive charge and will be naturally resistant to electrophilic attack. 

We know that in alkenes a double bond consists of a o and a n bond. The / -orbital tends to overlap as much as possible to make the bond strong because the greater the overlap of the two p orbitals, the stronger would be the bond. Maximum overlap occurs when the molecule becomes planar because in this condition the two p orbitals are parallel. Any distortion from the planar structure leads to decreasing overlap of the orbitals and a consequence of the weakening of the bond. The picture is represented as follows ... 

In order to make things a bit more concrete at this point we display in Figure 1 a sterically favorable configuration for a reactive ion pair (Tl). Only the 3d atomic orbitals most directly involved in the electron exchange are shown. The theoretical model developed here is based on a so-called "outer-sphere" mechanism, in which the inner-sphere reactants preserve their integrity in the course of the exchange reaction (aside from bond distortions associated with the activation step). The... 

Whereas FMO theory correctly predicts the regioselectivity for cycloadditions in simple alkyl-substituted olefinic systems,51,58 extension of similar calculations for cycloadducts (7a,b-lla,b)120 predicts the formation of regioisomer a, although, except in the case of 7 and 8, the b isomer is the predominant one. The differences between prediction and experiment in stereoselectivity have been attributed primarily to double bond rehybridization arising from double bond distortion in bridgehead olefins,142 which also explains their enhanced reactivity.96,120 Also double-bond deformation that will alter the normal mixing of alkyl substituent orbitals with localized rc-bond orbitals may explain the unexpected formation of 8b.120 Attempts to explain the formation of the b isomers, based on a two-step diradical mechanism, also have failed.120... 

In radially bonded clusters, the bonding cluster orbital energy levels lie lower when the number of nearest neighbors per atom is maximized, and this usually corresponds to close-packed high-symmetry structures. However, in clusters that do not correspond to completely filled, P and so on, shells, it may be more favorable for the cluster to distort and open up a significant HOMO-LUMO gap. The... 

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