Electronegativity of carbon

Using the relationship from the preceding section that the effective electronegativity of carbon in a C—H bond increases with its s character (sp < sp < sp), the order of hydrocarbon acidity behaves much like the preceding methane, ammonia, water, hydrogen fluoride series. 

A short digression is in order at this juncture. The electrophilic substitution of a vinylsilane is a very useful process because it is generally both regio- and stereospecific. The carbon-silicon bond is strongly polarized due to the high electronegativity of carbon (2.35) relative to silicon (1.64).67b A unique and important conse-... 

Because of the small difference between the electronegativities of carbon and hydrogen, alkanes have very small dipole moments, so small that they are difficult to measure. For example, the dipole moment of isobutane is 0.132 and that of propane is 0.085 Of course, methane and ethane, because of their symmetry, have no dipole moments. Few organic molecules have dipole moments greater than 7 D. 

The electronegativity of carbon is 2.5, whereas that of oxygen is 3.5. What type of bond would you expect to find in carbon monoxide ... 

When some boron atoms in non-classical boranes are exchanged by isolobal C+ units, the multicenter bonding MOs look qualitatively the same, but the contribution of carbon hybrid orbitals is larger than those from boron atoms [compare Figures 3.2-3(b) and (c)]. This polarization is due to the higher electronegativity of carbon versus boron atoms. 

The Pauling electronegativities of carbon and tellurium are, respectively, 2.5 and 2.1. This, in addition to the large volume of the tellurium atom (atomic radius 1.37, ionic radius 2.21), promotes easy polarization of Te-C bonds. The ionic character of the bonds increases in the order C(sp ) Te>C(sp ) Te>C(sp)-Te, in accordance with the electronegativity of carbon accompanying the s character (Table 1.1). 

The C—C and C—B interatomic distances in carboranes can also be related to the coordination numbers of the skeletal atoms. Two factors tend to make these distances shorter than the B —B distances in comparable boranes the preference of the carbon atoms for sites of low coordination number and the greater electronegativity of carbon than boron, which increases the electron density in the region of the carbon atoms and so strengthens the bonds that they form. Table IX lists some C—C distances for closo- and wido-carboranes 13, 20, 21, 26, 98,121,168) and metal-acetylene 50, 58,112) complexes, relating them... 

Because of the small difference between the electronegativities of carbon and hydrogen, alkanes have very small dipole moments, so small that they are difficult to measure. For... 

Note, however, that this places a formal positive charge on the oxygen and a formal negative charge on the carbon. If the electronegativities of carbon and oxygen were the same, carbon monoxide would have a sizable dipole moment in the direction... 

Proton transfers from carbon acids and to carbon bases are generally much slower. This is because the lower electronegativity of carbon requires that the negative charge on a carbon base be stabilized by electron delocalization. The consequent reorganization of structure and solvent may slow down the overall transfer rate. 

For the iodides, we know of no established thermochemical mimicry, although the comparative closeness of the electronegativities of carbon and iodine is suggestive. More precisely, the value for the enthalpies of zz-propyl to isopropyl iodide rearrangement, 10.0 ... 

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