Electronegativity definitions

Now, for electronegativity definition (3.17) we have the result (Putz, 2009a)... 

Remarkable, if the electronegativity definition relation (4.33) is formally integrated by taking into account the nature of the electronegativity potential as minus chemical potential for the system in focus, the total energy would result as an integral that would correspond to the summing (4.24). 

As noted before in the literature the Lapladan V bcp of 1 electron density pbcp at the BCP is correlated to pbcp (and hence to the BV), but obviously also to the degree of bond imiicity (which can e.g. be expressed by the electronegativity or hardness differences of catimi and anion). Using absolute electronegativity differences Xdiff (in eV) based on Mulliken s electronegativity definition [19]... 

In this equation, the electronegativity of an atom is related to its ionization potential, 1, and its electron affinity, E. Mulhken already pointed out that in this definition the ionization potential, and the electron affinity, E, of valence states have to be used. This idea was further elaborated by Hinze et al. [30, 31], who introduced the concept of orbital electronegativity. 

Another fundamental property of chemical bonds is polarity. In general, it is to be expected that the distribution of the pair of electrons in a covalent bond will favor one of the two atoms. The tendency of an atom to attract electrons is called electronegativity. There are a number of different approaches to assigning electronegativity, and most are numerically scaled to a definition originally proposed by Pauling. Part A of Table 1.6... 

A very simple definition of electronegativity also finds a foundation in DFT. The definition is... 

Besides the already mentioned Fukui function, there are a couple of other commonly used concepts which can be connected with Density Functional Theory (Chapter 6). The electronic chemical potential p is given as the first derivative of the energy with respect to the number of electrons, which in a finite difference version is given as half the sum of the ionization potential and the electron affinity. Except for a difference in sign, this is exactly the Mulliken definition of electronegativity. ... 

A further important concept related to electronegativity and polarity is that of acidity and basicity. We ll see, in fact, that much of the chemistry of organic molecules can be explained by their acid-base behavior. You may recall from a course in general chemistry that there are two frequently used definitions of acidity the Brtfnsted-Lowry definition and the Lewis definition. We ll look at the... 

In 1923. Lewis published a classic book (later reprinted by Dover Publications) titled Valence and the Structure of Atoms and Molecules. Here, in Lewis s characteristically lucid style, we find many of the basic principles of covalent bonding discussed in this chapter. Included are electron-dot structures, the octet rule, and the concept of electronegativity. Here too is the Lewis definition of acids and bases (Chapter 15). That same year, Lewis published with Merle Randall a text called Thermodynamics and the Free Energy of Chemical Substances. Today, a revised edition of that text is still used in graduate courses in chemistry. 

Electronegative adsorbate see electron acceptor adsorbate Electrophilic behaviour definition of, 156 examples of, 153, 286 global, 156 local, 157 mles of, 288, 303 Electrophilic reactions definition of, 156 list of, 286... 

These molecules must be regarded as essentially nonaromatic, although with some aromatic character. Tropolones readily undergo aromatic substitution, emphasizing that the old and the new definitions of aromaticity are not always parallel. In sharp contrast to 44, cyclopentadienone (46) has been isolated only in an argon matrix below 38 Above this temperature, it dimerizes. Many earlier attempts to prepare it were unsuccessful. As in 44, the electronegative oxygen atom draws electron to itself, but in this case it leaves only four electrons and the molecule is unstable. Some derivatives of 46 have been prepared. ... 

There is little information for fluoro-substituted sulfinyl groups. Values of a and ffp for SOCFj based on benzoic acid ionization are 0.63 and 0.69 respectively , compared with values of about 0.52 and 0.49 for SOMe (Table 3). Thus the electronegative fluorine somewhat enhances the electron-attracting influence of the sulfinyl function and makes the order more definitely sulfur lone pair to engage in 7t(pp) conjugation. Values of and ffp for SOCF3 based on anilinium ion dissociation are 0.76 and 1.05 respectively . An increase of 0.13 as between and [Pg.509]

The E-state indices are atomic descriptors composed of an intrinsic state value I and a perturbation AI that measures the interactions with all other atoms in a molecule. The Kier-Hall electronegativity is the starting point in the definition of the intrinsic state of an atom, which encodes its potential for electronic interactions and its connectivity with adjacent atoms. The intrinsic state of an atom i is [19, 21] ... 

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). 

These definitions are clear, but they do not apply to the vast majority of real molecules in which the bonds are neither purely ionic nor purely covalent. Lewis recognized that a pair of electrons is generally not shared equally between two electrons because the atoms generally have different powers of attracting electrons, that is, they have different electronegativities, giving charges to both atoms. Such bonds are considered to have some covalent character and some ionic character and are known as polar bonds. 

The definition (3.60) can even be extended to the lone-pair case, in which the ligand is nonexistent, by recognizing that this corresponds to the ionicity limit / = — 1. In this case Eq. (3.60) gives for the formal lone-pair electronegativity ... 

Heats of formation can be derived by reversing the Pauling definition of electronegativity, but empirical corrections are needed to allow for extra strength of multiple oxygen or nitrogen bonding, as in... 

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