Orbitals electronegativity effects

The PEOE method leads to only partial equalization of orbital electronegativities. Thus, each atom of a molecule retains, on the basis of Eq. (12), a residual electronegativity that measures its potential to attract further electrons. It has been shown that the values of residual electronegativities can be taken as a quantitative measure of the inductive effect [35]. 

The hypothesized delocalization of lone pair electrons in the above silicon compounds is supported by the lowered basicity of the silyl compounds as compared to the corresponding carbon compounds. This reduced basicity is contrary to that expected on the basis of electronegativity effects operating through the a system since silicon is less electronegative than carbon. It is consistent with an internal Lewis acid-base interaction between the nitrogen and oxygen lone pairs and empty acceptor d orbitals on the silicon. Experimentally this reduced basicity is shown by the absence of disiioxane adducts with BF3 and BO ... 

With simple aromatic compounds (Tables XVII and XVIII) the effect of structure on sensory qualities is easily recognizable, too. In order to determine electrophilic and nucleophilic centers in aromatic compounds their charge distributions were calculated. The values for the atomic charges were obtained from a computer program which is based on a model for partial equalization of orbital electronegativity (26, 27). This model was extended to1T-systems (28). 

Three p orbitals, all aligned parallel to one another, make up the allyl unit and produce three molecular orbitals. The MOs for the following systems differ from the completely carbon allylic system only in the previously discussed electronegativity effects (the bonding MOs will have a larger contrihution from the heteroatom p orbital and the antibonding MOs will have a lesser contribution. Section 2.3). 

Raimondi, 1963 Clementini et al., 1967) Principal Quantum Number (n) Orbital Exponent ( ) Effective Atomic Charge (Z ) Number of Employed [s+p] Valence Electrons (N ) Electronegativity (4.3) and Chemical Hardness (4.251) based on Ej erimental Ionization Potential (IP) and Electronic Affinity (EA) (Ghosh Biswas, 2002), Maximum Radii for Vanishing Radial Distribution of Electronic... 

Proton transfer from water or other acid to pyridine does not involve the electrons of the aromatic sextet. Why, then, is pyridine a considerably weaker base than aliphatic amines The answer is that the unshared pair of electrons on the pyridine nitrogen lies in a relatively electronegative sp hybrid orbital, whereas in aliphatic amines, the unshared pair lies in an sp hybrid orbital. This effect decreases markedly the basicity of the electron pair on an spi hybridized nitrogen compared with that on an sp hybridized nitrogen. 

Levin, C. C. "A Qualitative Molecular Orbital Picture of Electronegativity Effects on XH3 Inversion Barriers." /. Am. Chem. Soc., 97,5649 (1975). 

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