Hybrid orbitals methyl compounds

The geometry of most organosUanes is tetrahedral using the sp hybridized orbitals on sihcon. Like carbon, optically active silanes are possible when central chirality exists. A series of monofunctional optically active silanes can be prepared and used for stereochemical studies. These are the methyl(naphthyl)phenylsilyl derivatives, which are commoifly abbreviated to R3 Si X. Together with the similar germanium compound, the isoconfigurational series of compounds are shown in Figure 1. 

This electron-deficient unit does not obey the octet rule, as it does not have enough electrons to form four two-centre two-electron bonds around each carbon atom. The interaction between an sp hybrid orbital of a methyl group with three 2s orbitals of the Li atoms form a symmetric four-centre two-electron bonding orbital, which accounts for the bonding in this compound. 

The only well-defined examples of lead(II)organometallic compounds are bis(cyclopenta-dienyl)lead(n) and its ring methyl derivative s. In the gas phased this has a bent sandwich structure as shown in Fig. 1 (a). Such a structure is also proposedso to account for the solution spectra of (CsHs)2Pb, where the two rings are believed bonded to two sp lead hybrid orbitals, and a further sp orbital contains a non-bonding pair of electrons. Such a bonding situation is in accord with the crystal structure of the orthorhombic form shown in Fig. 1 (b). 

There are also some couplings in which hydrazones are formed but for which the azo tautomer is not detectable and probably does not exist. This is the case in some coupling reactions involving methyl groups of aromatic heterocycles (see, for example, 12.48 and 12.49 in Sec. 12.5). Replacement of a methyl proton by an arylazo group (Scheme 12-3) would result in an azo compound containing an sp3-hybridized — CH2 — group (12.1). The latter is less stable than the tautomeric hydrazone (12.2), in which there is a n-n orbital overlap from the heteroaromatic to the aromatic system. 

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