Carbon electronegativity value

Regression analyses revealed systematic differences between experimental log P and log P calculations based on the summation of fragment values. These differences could be attributed to chemical characteristics of the molecules, which in turn allowed the definition of correction rules such as chain conjugation, electronegativity facing bulk or the proximity effect, which describes the presence of electronegative centers in a molecule separated by one or two carbons. Correction values needed for log P calculation were shown to represent multiples of a constant value of 0.289, which is known as the magic constant (CM). 

Fig. 35. (a) Correlation between the photolysis rate of halomethyl-cobalamins and the electronegativity of the alkyl ligand. (The electronegativity values are shown as the sums of the Pauling electronegatives of the atoms attached to the methyl carbon.) (b) Correlation between pKa for displacement of benzimidazole and alkyl group electronegativity for a series of halomethyl-cobalamins... 

The degree of positive or negative character at carbon depends on the difference in electronegativity between the carbon and the atoms to which it is attached. From Table 1.2, we find the electronegativity values for the atoms contained in the molecules given in the problem are ... 

Sequence 16 clearly demonstrates electrophilic attack by ozone in these reactions. As noted by Jensen and Rickborn (2), the rate of electrophilic cleavage of a carbon-metal bond increases as the polarization of that bond increases. This, in turn, is a direct consequence of the electronegativity of the second atom attached to mercury. The following representations, based on Pauling electronegativity values, illustrate this relationship. 

Fig. 1.43 Allen electronegativity values and Pauling-based values for carbon hybrids...

Q From a consideration of the Pauling electronegativity values, predict the charge distribution in the carbon silicon bond. 

Electronegativity values are used as a guideline to indicate whether the electrons in a bond are equally shared or unequally shared between two atoms. For example, whenever two identical atoms are bonded together, each atom attracts the electrons in the bond to the same extent. The electrons are equally shared, and the bond is nonpolar. Thus, a carbon-carbon bond is nonpolar. The same is true whenever two different atoms having similar electronegativities are bonded together. C-H bonds are considered to be nonpolar, because the electronegativity difference between C (2.5) and H (2.2) is small. 

Carbon, the most important element for our purposes, has an electronegativity value of 2.5. Any element more electronegative than carbon has a value greater than 2.5, and any element less electronegative than carbon has a value less than 2.5. 

What properties would you predict for alkanes All of the bonds in these hydrocarbons are between either a carbon atom and a hydrogen atom or two carbon atoms. Are these bonds polar Remember, a bond between two atoms is polar only if the atoms differ by at least 0.5 in their Pauling electronegativity values. Carbon s electronegativity value is 2.55, and hydrogen s is 2.20, so a C—H bond has a difference of only 0.35. Thus, it is not polar. A bond between two identical atoms such as carbon can never be polar because the difference in their electronegativity values is zero. Because all of the bonds in alkanes are nonpolar, alkane molecules are nonpolar. 

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