Group-VB—carbon bonds

Cleavages of carbon-group-VB element bonds to give organolithiums occur with yields of C HsLi (X, yield)i N, 25 P, 64 As, 76 Sb, 62%. Usually, the Li salt of the group-VB element is the desired product, and the organolithium is a byproduct ... 

The cleavage of carbon-group-VIB, -VB or -IVB element bonds to give organolithiums is directly analogous to the Li cleavage of carbon-halogen bonds (see 5.5.2.2.1) ... 

Atomic charges have been used to analyze the nature of the interaction between the nitrogen and carbon groups in amides. In VB language this interaction is described in terms of resonance. These resonance structures account for the most characteristic properties of amides. They are quite polar and react with protons and Lewis acids at oxygen, but not at nitrogen. The partial C=N double bond character also accounts for the observed rotational barrier of about 18kcal/mol. 

Hybrid S values for any desired ty >e of hybrid can be obtained very easily from the tables as simple linear combinations of nonhybrid 5 values. It is shown how 5 values corresponding to orthogonalizerl Slater AO s and approximate S values for SCF (self-consistent-field) AO s can also be obtained as linear combinations of the Slater-AO S values. 5 values for carbon-carbon 2pa- and 2/r-bonds using SCF carbon AO s have been computed (see Table in Section Vb) they correspond to stronger overlap than for Slater AO s. Non-locaHaed MO group-orbital S values are also discussed, and are illustrated by an application to H20. The use of the tables to obtain dipole moments for electronic transitions in certain cases is also mentioned. The use of the tables to obtain S values for various specific atom-pairs and bond-types, and resulting conclusions, will be discussed in another paper. 

A silyl substituent can stabilize the positive charge in a carbocation if the spatial arrangement allows overlap of the C-Si a-bond and the vacant p-orbital at the C -carbon. The hyperconjugative interaction of a p-silyl group, as shown in the MO- and VB-structures in Fig.l, is called the P-silyl... 

Distortion of this type is to be expected as a result of normal steric interaction, particularly when bulky groups are attached to the olefinic bond. However in complexes such as [Pt(PPh3)2TCNE] (D.XII) the distortion from planarity is very large indeed. A VB interpretation of such distortions would describe them as the result of a partial rehybridization of the orbitals of the carbon atoms from sp2 to sp3 for olefin complexes and sp to sp2 for acetylenes. In some molecules (e.g. [Co4(CO)10(EtC CEt)] (D. XXV)) this is a reasonably acceptable explanation but it is not so helpful when distortions are small. 

These molecules, propenal, methoxyethene, and etheneamine, show how we can apply VB theory and resonance to questions of reactivity. We looked at how structure and conjugation affect electron density and bond formation in both the reactant and the intermediate. When VB theory indicates that the particular disposition of function groups will change the electron distribution relative to an unsubstituted molecule, we can expect to see those differences reflected in altered reactivity. For propenal, the electron withdrawal by the formyl group causes decreased reactivity toward electrophiles and increased reactivity toward nucleophiles. For methoxyethene and ethenamine, the electron release of the substituents is reflected by increased reactivity toward electrophiles with strong selectivity for the P-carbon. 

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