Orbitals maximum overlap

Thus, neglecting the doubly occupied orbitals, a subspace of the spatial parts of the t orbitals and a subspace of the spin-down ones are considered. In the next subsection, a basis will be developed dealt with, the orbitals of which are called maximum overlap orbitals. ... 

All atoms taking part in the resonance, that is, covered by delocalized electrons, must lie in a plane or nearly so (see p. 42). This, of course, does not apply to atoms that have the same bonding in all the canonical forms. The reason for planarity is maximum overlap of the p orbitals. 

A basis set ofhybrid AOs,having o, tt or n character, is prepared by the Slater s,p valence set according to the maximum overlap criterion [31,46]. An extension to d orbitals is in progress. 

It is thus evident that the reaction path is controlled by the frontier-orbital interaction. The position of reaction will be determined by the rule of maximum overlapping of frontier orbitals, that is, HO and LU MO s of the two reacting molecules. Sometimes SO takes the place of HO or LU in radicals or excited molecules. Hence, the general orientation principle would be as follows ... 

Localized bonding orbitals are then constructed from a linear combination of the orbital on each of the paired atoms. To do this we use the principle of maximum overlap, which states... 

Figure 3.13 shows approximate representations of the 2px and 2p orbitals. To construct the two bonding orbitals b] and b2 we place the H atoms along the directions of the 2p and 2pv orbitals of the O atom to give maximum overlap of a Is orbital of H with the 2p, and 2py 0 orbitals (Figure 3.13). This bonding model implies a bond angle of 90° for the water molecule, which is not in very good agreement with the observed angle of 104.5°.

Maximum overlap between the p orbitals of a k bond occurs when the axes of the... 

Therefore, in the final analysis, the quadruple bond consists of one a bond, two it bonds, and one S bond. The configuration in which the Cl atoms are in eclipsed positions provides maximum overlap. From the rather intuitive analysis provided here, it is possible to arrive at a qualitative molecular orbital diagram like that shown in Figure 21.23 to describe the Re-Re bond. 

Although structures involving methyl groups bonded simultaneously to two carbon atoms by means of an overlap between the hydrogen orbitals and the />-orbitals of the carbon atoms may be readily enough assimilated, the state of structural theory is such that most of the cyclic intermediate or transition state structures are dubbed non-classical. In many cases they are best depicted by molecular orbitals, usually by diagramming the component atomic orbitals in the best position for overlap. Since maximum overlap of the component atomic orbitals imposes certain geometric requirements, pre-... 

Six-Membered Ring (endo-Cyclic). All the previous discussion of stereo-attack is based on steric hindrance, but in the case of a six-membered ring (endo-cyclic) enolate, the direction is affected simultaneously by stereo-electronic effects (Scheme 2-4).10 In the transition state, the attacking electrophiles must obey the principle of maximum overlap of participating orbitals by perpendicularly approaching the plane of atoms that constitute the enolate functional group. Electrophile attacks take place on the two diastereotopic... 

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 ... 

The phenyl substituent in cation 8a is oriented almost perpendicular to the plane spanned by the two silicon atoms and the atom. This ground state conformation provides maximum overlap between the empty 2p orbital at... 

Both are essentially planar, i.e. sp hybridised, at the radical carbon atom for only in this configuration is maximum pjn orbital overlap— with consequent stabilisation—possible. The stability of a radical increases as the extent of potential delocalisation increases thus PhjCH is more stable than PhCHj , and PhjC (c/. p. 300) is a pretty stable radical. 

Molecular orbital theory of the covalent bond shows a direct relationship between the extent of the overlap of two atomic orbitals and the bond strength. The larger the overlap, the stronger the bond. Maximum overlapping would produce the strongest bond and the most stable system. Maximum overlap of the H and O atomic orbitals... 

Another important point deals with selectivity in the abstraction of -protons on equally substituted carbons. In a iyw-periplanar transition state as described above, the minimization of energy concept implies proton abstraction with a maximum of orbital overlap and a minimum of molecular deformation. Consequently, conformations possessing the more acute dihedral angles for bonds H —C—C—O wiU be favored (Scheme 2l/. 

As we have pointed out many times previously, the columns of the standard tableaux functions are antisymmetrized, and the orbitals in a column may be replaced by any linear combination of them with no more than a change of an unimportant overall constant. In this case, consider a linear combination that has two hybrid orbitals that point directly at the H atoms in accord with Pauling s principle of maximum overlap. Using the parameter

[Pg.180]

C-alkylation is predicted to occur via attack on the enolate carbon perpendicular to the C — C — O plane for maximum overlap of the re-system. Such a transition state 5 can be easily achieved when the ring to be formed is six-membered. In the five-membered ring closure there is less strain in a nucleophilic substitution involving the lone-pair orbital on oxygen. 

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