The concept of electronegativity has strongly evolved since its “early definition in the nineteen thirties by Pauling” [1]. At the beginning, electronegativity was designed to characterize the behavior of an atom within a molecule from its properties as an isolated atom. In the nineteen fifties, two important contributions have been published; (i) the electronegativity equalization principle; (ii) the definition of the absolute electronegativty [3]. The former paper by Sanderson indicates that when reagents react with each other, the electronegativity equalizes all over the system. The latter article by Iczkowski and Margrave provides an absolute definition of electronegativity based on the energy variation of the system during this equalization. In the last three decades, along with the development of Density Functional Theory of Chemical Reactivity [4] (also called conceptual DFT), the concept of electronegativity has been dug out again and quite recently the concept of local electronegativity has been put forward [5,6]. The aim of this talk is to frist review the concept of electronegativity and then define the notion of local electronegativity. It is also to show how this concept is related to the dual descriptor [7,8] and how it can help understanding the regioselectivity of organic reactions. Some examples, such as the markonikov’s rule or the orientation of Electrophilic Aromatic substitution [9], will be presented. Photochemical reaction will be illustrated as well [10].  

[1]    Pauling, L. J. Am. Chem. Soc.  1932 , 54, 3570 

[2]    Sanderson, R.T. J. Am. Chem. Soc. 1952, 74, 272

[3]    Iczkowski, R.P.; Margrave, J. L. J. Am. Chem. Soc.  1961 , 83, 3547  

[4]    Geerlings, P.; De Proft, F.; Langeneaker, W. Chem. Rev. 2003, 103, 1793

[5]    Ayers, P. W. Theor. Chem. Acc. 2007, 118, 371-381

[6]    Morell, C.; Ayers, P.W.; Grand, A.; Chermette, H. Phys. Chem. Chem. Phys. 2011, 13, 9601

[7]    Morell, C.; Grand, A.; Toro-Labbé, A. J. Phys. Chem. A . 2005, 109, 205

[8]    Tognetti, V.; Morell, C.; Ayers, P.W.; Joubert, L.; Chermette, H. Phys. Chem. Chem. Phys. 2013, 15, 14465 

[9]    Morell, C.; Grand, A.; Gutiérrez-Oliva, S.; Toro-Labbé, A. Theoretical and Computational

Chemistry. Editor: Peter Politzer and Z.B. Maksic. Vol 17: Theoretical Aspects of Chemical

Reactivity. Volume Editor: Alejandro Toro-Labbé. Elsevier. 2006

[10]  Morell, C.; Labet, A.; Grand, A.; Ayers, P.; Geerlings, P.; De Proft, F.; Chermette, H. J. Chem. Theo. & Comp. 2009, 5, 2274