Reactivity Energetic Indices

2 MODELING AROMATICITY BY CHEMICAL HARDNESS 4.2.1 REACTIVITY ENERGETIC INDICES 

Nowadays, competitive software is available to perform advanced calculations with high accuracy in order to assess the aromaticity of different systems. From our experience in teaching, today s students are able to use these computer programs but encounter difficulties in the interpretation of the results obtained. In order to help them gaining some insights, we apply Hiickel molecular orbital theory (HMO), highly didactical, by comparison with a modem one, density functional theory (DFT), to explain the reactivity of some aromatic hydrocarbons and heteroaromatic compounds. 

The Hiickel method is simple and has been in use for decades. It is at anyone hand as a starting point to the understanding of the methods without 

On the other hand, DFT is among the most popular and versatile methods available in computational chemistry (Kohn et al., 1996). The calculations performed with DFT directly reflect the electronic density influence of a chemical stmcture towards its reactivity (Kohn and Sham, 1995). Mainly, the electronic energy is approximated by various density functional terms the present discussion follows (Putz, 2008a, 2012a) 

The purpose of this analysis is to correlate some accessible quantum chemical results with physico-chemical properties of some aromatic compounds. The systems presented are hydrocarbons (aromatic aimu-lenes), amines, moleeules, ions, hydroxyarenes, and heterocycles with nitrogen, all of them selected according to their industrial significance. For example, by diazotization and coupling reactions the aromatic amines and phenols lead to azo dyes. The heterocyclic compounds take part in 

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Notice that since rj > 0, we always have AE < 0, i.e., the charge transfer process is energetically favorable. We proposed the new density functional theory (DFT) reactivity index, electrophilicity index oj as... 

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