Bonding in organolithium compounds

The carbon-lithium bond in organolithium compounds is polar covalent, with a partial negative charge on carbon, making it nucleophilic and basic. 

Currently, the analysis of the molecular structure based on topological examination of the electron density has gained wide acceptance [19,21-26]. This approach has led to some unexpected conclusions as to the character of bonds in certain compounds. For example, a study of the C—Li bonds in organolithium compounds [27] has shown that in compound V, notwithstanding the large distance between the carbon atoms and C4 equal to 3.121 A, there... 

The magnitude of the chemical shift anisotropy depends on the bonding situation and the nucleus gyromagnetic ratio. Since the bonds formed by lithium in organolithium compounds or other lithiated systems are mainly ionic, the anisotropy of the lithium chemical shift is generally small. It is more pronounced for Li than for Li. Li spectra are dominated by the quadrupolar effect and the CSA contribution to the Li lineshape is often negligible. Exceptions are compounds with poly-hapto bound lithium, such as... 

A handicap of Grignard reagents in the field of anionic polymerization is certainly their low reactivity toward nonpolar double bonds. Unlike organolithium compounds, organomagnesium compounds are nornally inert toward monomers sueh as styrene or butadiene. Thus, their scope in the field of anionic block-copolymerization is quite limited. 

The crystal and molecular structures of 105 have been determined it has an anomalous structure with very short intermolecular Te—N bonds of 2.4 A.159 Mass spectral,28 13C- and 77Se-NMR data160 of 1,2-benzisoselen-azoles have been reported. The intramolecular Se—N bond in these compounds is weaker than in 1,2-benzisothiazoles and is readily cleaved by organolithium reagents.161162... 

The car bon-metal bonds of organolithium and organomagnesium compounds have appreciable carbanionic character. Carbanions rank anong the strongest bases that we ll see in this text. Their- conjugate acids are hydrocarbons—very weak acids indeed. The equilibrium constants for ionization of hydrocarbons are much smaller than the A s for water and alcohols, thus hydrocarbons have much larger pA s. 

RR C=NLi) . They can be prepared in high yield either by the addition of an organolithium compound across the triple bond of a nitrile (equation (1)) or by lithiation of a ketimine (equation (2)). 

J-Oxygen-functionalised sp3 organolithium compounds react with alkenyl-carbene complexes to generate the corresponding cyclic carbene complexes in a formal [3+3] process (see Sect. 2.8.1). In those cases where the organolithium derivative contains a double bond in an appropriate position, tricyclic ether derivatives are the only products isolated. These compounds derive from an intramolecular cyclopropanation of the corresponding cyclic carbene complex intermediate [89] (Scheme 83). 

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