Silicon orbital interactions with

In some situations, using this option may be important. For example, ifp orbitals on electronegative atoms interact with d orbitals, (as for a silicon atom bonded to an amine group), you may want to include d orbitals. 

The P-effect, the interaction of a P-carbon silicon a-bond with the vacant p-orbital at the C+ carbon, is called hyperconjugation i.e. the conjugation of the... 

These studies show the simultaneous lengthening of the silicon-leaving group bond as the silicon-nucleophile interaction increases. Molecular orbital calculations at the STO-3G level by Deiters and Holmes29 also show that as the nucleophile approaches from an apical position, the trans axial bond to the leaving group increases in length. However, there is little conclusive evidence as to whether a pentacoordinate intermediate with a finite lifetime is involved in such invertive processes. 

In contrast to cyclotetrasilenylium ion 70, the four-membered ring of cyclotetrasilenyl radical 72 is almost planar with a dihedral angle of 4.7°.43 The distances between unsaturated silicon atoms of 72 (2.226(1) and 2.263(1) A) are also intermediate between the Si = Si double bond and the Si Si single bond in 49. In contrast to cation 70, radical 72 has a long interatomic distance between terminal unsaturated silicon atoms [3.225(2) A] indicating no significant 1,3-orbital interaction in 72.27... 

A mechanism for the disproportionation reaction has been suggested which involves the formation of an intermediate species (or transition state) in which a lone pair of electrons from the cyanide group of one molecule interacts with vacant silicon 3d orbitals of an adjacent molecule (or more probably, partly with a d orbital of each silicon atom simultaneously), the silicon-silicon bond being thereby weakened. 

Of the two explanations advanced, one is the usual ir-bonding concept involving d orbitals of the third-row elements (34), whereas the other refers to a more electrostatic picture (60). The lone pair of electrons at the carbanion is supposed (a) to interact with the suitable empty orbitals of silicon and (b) to suffer much less repulsive interactions from bond pairs in the presence of the larger elements. Both arguments call for the planar or quasi-planar geometry of the carbanion, which is observed in phosphorus ylides. 

Two transition structures with a retention (192, TSret) and an inversion (193, TSinv) configuration (Figure 2) were optimized for 1,3-silyl migration in allylsilane at HF/6-31G, MP2/6-31G and DFT/6-31G levels. The TSjnV 193 was found to be a distorted trigonal bipyramid (TBP) around the silicon with the two allylic carbons at the equatorial positions different from the TS illustrated by Kwart and Slutsky297,302, while 192 has a distorted square pyramid (SP) structure around silicon. Analysis of the orbital interaction in the transition states showed that the major stabilization of 193 was caused by the MO interaction as predicted by the Woodward-Hoffmann rules, while the major stabilization in 192 was ascribed to the subjacent orbital control. 192 was more stable than 193 at... 

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