Carbon electronegativity

The methyl protons of TMS are in a more electron-dense environment than are most protons in organic molecules, because silicon is less electronegative than carbon (electronegativities of 1.8 and 2.5, respectively). Consequently, the signal for the methyl protons of TMS is at a lower frequency than most other signals (i.e., it appears to the right of the other signals). 

The electronegativity difference between carbon (electronegativity 2.5) and oxygen (electronegativity 3.5) is 1, so the C=0 bond is polar ... 

The general observation that replacement of a hydrogen or carbon attached to the carbon-carbon double bond by halogen results in retardation of electrophilic addition reactions is justified by arguing that there is decreased electron density in the double bond. That is, halogen inductively withdraws electrons better than hydrogen or carbon (electronegativity, Chapter 1). 

The unequal distribution of charge produced when elements of different electronegativities combine causes a polarity of the covalent bond joining them and, unless this polarity is balanced by an equal and opposite polarity, the molecule will be a dipole and have a dipole moment (for example, a hydrogen halide). Carbon tetrachloride is one of a relatively few examples in which a strong polarity does not result in a molecular dipole. It has a tetrahedral configuration... 

The other more electronegative elements are non-metals and form oxides which are entirely covalent and usually acidic. For example, sulphur yields the oxides SO2 and SO3, dissolving in bases to form the ions SO3 and SO4" respectively. A few non-metallic oxides are often described as neutral (for example carbon monoxide and dinitrogen oxide) because no directly related acid anion is known to exist. 

Previous studies with a variety of datasets had shown the importance of charge distribution, of inductive effect), of r-electronegativity, resonance effect), and of effective polarizability, aeffi polarizability effect) for details on these methods see Section 7.1). All four of these descriptors on all three carbon atoms were calculated. However, in the final study, a reduced set of descriptors, shown in Table 3-4, was chosen that was obtained both by statistical methods and by chemical intuition. 

Fluorine is the most electronegative and reactive of all elements. It is a pale yellow, corrosive gas, which reacts with most organic and inorganic substances. Finely divided metals, glass, ceramics, carbon, and even water burn in fluorine with a bright flame. 

The nitrogen ending atoms being more electronegative possess a tt electronic density greater than that of the carbon atoms directly linked to them. 

The direction of the dipole moment is toward the more electronegative atom In the listed examples hydrogen and carbon are the positive ends of the dipoles Carbon is the negative end of the dipole associated with the C—H bond... 

With four bonds carbon already has eight electrons The remaining 12 electrons are added as indicated Both oxygens have eight electrons but nitrogen (less electronegative than oxygen) has only six... 

Most of the time we are concerned only with whether a particular reaction is an oxidation or reduction rather than with determining the precise change m oxidation num ber In general Oxidation of carbon occurs when a bond between carbon and an atom that IS less electronegative than carbon is replaced by a bond to an atom that is more electronegative than carbon The reverse process is reduction... 

Notice that this generalization follows naturally from the method of calculating oxida tion numbers outlined m Table 2 5 In a C—C bond one electron is assigned to one carbon the second electron to the other In a bond between carbon and some other ele ment none of the electrons m that bond are assigned to carbon when the element is more electronegative than carbon both are assigned to carbon when the element is less elec tronegative than carbon... 

Carbon-fluorine bonds are quite strong (slightly stronger than C—H bonds) and like polyethylene Teflon is a very stable inert material We are all familiar with the most characteristic property of Teflon its nonstick surface This can be understood by com paring Teflon and polyethylene The high electronegativity of fluorine makes C—P bonds less polarizable than C—H bonds causing the dispersion forces m Teflon to be less than those m polyethylene Thus the surface of Teflon is even less sticky than the already slick surface of polyethylene... 

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