Electrophilicity global descriptors

A review of literature would show that a suite of QC descriptors have also been used in QSARs for biological and toxicological correlations. Such indices have been derived both from semiempirical and ab initio (Hartree Fock and density functional theory) methods. In particular, in our QSAR studies, we have used the following levels of QC indices local and global electrophilicity indices [11],... 

Describes various global reactivity descriptors, such as electronegativity, hardness, and electrophilicity... 

Roy, R.K., Usha, V., Paulovic, J. and Hirao, K. (2005) Are the local electrophilicity descriptors reliable indicators of global electrophilicity trends J. Phys. Chem. A, 109, 4601 606. 

In these cases, the chlorobenzenes act as electron acceptors while the benzidine molecule behaves as an electron donor. The effect of chlorine substitution on the aromaticity of the planar benzene ring of the chlorobenzene derivatives is assessed from the nucleus independent chemical shift (NICS) criterion proposed by Schleyer et al. [338]. Among the various global and local molecular descriptors, electrophilicity (m) is found to be the most appropriate reactivity parameter regarding toxicity... 

In this work, we have developed a model for the evaluation of proton affinity in terms of some akin conceptual reactivity descriptors which can be concepmally linked and associated with the physico-chemical process of protonation. The akin descriptors are the ionization energy (I), the global softness(S), the electronegativity (x), and the global electrophilicity index (co). 

Conceptual density functional theory has been quite successful in providing quantitative definitions for popular qualitative chemical concepts like electronegativity , hardness and electrophilicity . It has also been found to be useful in providing firm theoretical bases for the associated electronic structure principles. Various global and local reactivity descriptors " have played an important role in analyzing bonding, reactivity, stability, interactions and aromaticity in a variety of many-electron systems as well as a host of their physico-chemical properties. 

The global electrophilicity index (q), introduced by Parr (Parr, et al, 1999) is a useful descriptor of the reactivity that allows a quantitative classification of the global electrophilicity character of a molecule within a unique scale. Current studies based on the DFT and applied to DA reactions, have shown this classification of the diene/ dienophile pair is a powerful tool to predict the feasibility of the process and the type of mechanism involved. This index defined as Eq. 3... 

Useful information about polarity of de DA processes may be obtained from the difference in the global electrophilicity power of the reactants. This difference has been proposed as a measure of the polar character of the reaction. On the other hand, local reactivity indexes are associated with site selectivity in a chemical reaction. These descriptors should reflect the sites in a molecule where the reactivity pattern stated by the global quantities should take place. For instance, an important local reactivity parameter was introduced by Parr et al., and it was defined as the Fukui fimction (Domingo, et al, 2002)... 

Specifically the reactions of 2-nitrofuran, methyl 5-nitro-3-furancarboxylate, and methyl 5-nitrofuran-2-carboxylate, respectively, and Danishefsky s diene were studied using the hardness, the polarizability and the electrophilicity of the corresponding DA primary adducts as global reactivity indexes. The experimentally observed products for these DA reactions using different conditions were indicated in the Figure 21, and related experiments. It has been demonstrated that both the hardness as well as the electrophilicity power of adducts are appropriate descriptors for predicting the major product of the reactions at least in the cases study here. (Brasca, et al, 2011)... 

Roy RK (2004) On the reliability of global and local electrophilicity descriptors. J Phys Chem... 

Parr et al. [6] defined one more global reactivity descriptor of atoms and molecules. The parameter was labeled as global electrophilicity index, (co). This has special reference to correlate the reactivity of the reference molecules, a drug, with a biomolecule when the reaction becomes either electrophilic or nucleophilic. The proposed ansatz electrophilicity index (co) is defined as... 

TABLE 2 Calculated global reactivity descriptors global hardness (ii), global softness (S), electrophilicity index (oo), electronegativity (x) of the mesoionic heterocychc compounds. 

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