Atom-Bond Electronegativity Equalization

Yang ZZ, Wang CS (1997) Atom-bond electronegativity equalization method. 1. Calculation of the charge distribution in large molecules. J Phys Chem A 101(35) 6315-6321... 

Wang CS, Li SM, Yang ZZ (1998) Calculation of molecular energies by atom-bond electronegativity equalization method. Theochem J Mol Struct 430, 191-199... 

Wang CS, Yang ZZ (1999) Atom-bond electronegativity equalization method. II. Lone-pair electron model. J Chem Phys 110(13) 6189-6197... 

Cong Y, Yang ZZ (2000) General atom-bond electronegativity equalization method and its application in prediction of charge distributions in polypeptide. Chem Phys Lett 316(3-4) 324-329... 

Yang ZZ, Wang CS (2003) Atom-bond electronegativity equalization method and its applications based on density functional theory. J Theor Comput Chem 2(2) 273-299... 

Yang ZZ, Wu Y, Zhao DX (2004) Atom-bond electronegativity equalization method fused into molecular mechanics. I. A seven-site fluctuating charge and flexible body water potential function for water clusters. J Chem Phys 120(6) 2541-2557... 

The LIE method has also been used with continuum electrostatic methods. Nicolotti et al. (27) have published a nice report on this use of the LIE method for screening benzamidine inhibitors of thrombin. Another recent study used the atom-bond electronegativity equalization method on force field with the generalized Born (GB) continuum electrostatics approach to predict binding free energies of HIV-1 protease inhibitors (28). 

Z. Z. Yang and X. Li,/. Chem. Phys., 123(9), 94507 (2005). Molecular-Dynamics Simulations of Alkaline-Earth Metal Cations in Water by Atom-Bond Electronegativity Equalization Method Fused into Molecular Mechanics. 

A chemical bond exhibiting 100% covalent character and 0% ionic character occurs between identical nonmetals atoms in which the difference in electronegativity (AEN) is zero. An example is the H-H bond. There are atoms with essentially the same electronegativity, e.g. N and Cl both have an electronegativity equal to 3.0 to 2 significant figures, so the N-Cl bond would exhibit close to 100% covalent character and 0% ionic character . 

However, at first sight the ionic-resonance model would not seem applicable to I3- and related symmetric hypervalent species, because extreme I+I ionicity differences would not be expected between central and terminal atoms of intrinsically equal electronegativity. Nevertheless, we shall show that the complementary bidirectional resonance stabilization motif (3.188) can lead to effective three-center bonding even if central and terminal atoms are of equal electronegativity. 

These descriptors have been widely used for the past 25 years to study chemical reactivity, i.e., the propensity of atoms, molecules, surfaces to interact with one or more reaction partners with formation or rupture of one or more covalent bonds. Kinetic and/or thermodynamic aspects, depending on the (not always obvious and even not univoque) choice of the descriptors were hereby considered. In these studies, the reactivity descriptors were used as such or within the context of some principles of which Sanderson s electronegativity equalization principle [16], Pearson s hard and soft acids and bases (HSAB) principle [17], and the maximum hardness principle [17,18] are the three best known and popular examples. 

In these molecules the electronegativity difference between the atoms which form the bond is zero and therefore the charge distribution within the bond is equal. 

The fluorines are the most electronegative atoms present, and the bonds to them are polar covalent. The only nonpolar compound is the result of the polar C-F bonds pulling equally in opposite directions. 

Formal charge is very different from oxidation state, which is assigned by apportioning electrons in a bond to wire electronegative atom rather than equally. Both are artificial assignments. The concept of resonance is one way of overcoming some limitations of the localised electron pair model. 

Stretching vibrations of atoms with different electronegativity modulate the molecular dipole moment, thus, they show strong infrared bands. Vibrations of bonds between equal atoms show infrared bands of very low intensity, however, they modulate the molecular polarizability and therefore show strong Raman bands. The intensity of the bands in the infrared spectrum is zero - the bands are forbidden in the infi ared spectrum - if the environment of both atoms is equivalent by symmetry. 

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. 

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