Why Benzene prefers to substitute and an Olefin likes to add?
Hückel MQ (HMO) theory,1,2 predicts that pi benzene is more stable than three pi ethylenes. This conclusion seems to be compatible with the fact that the heat of hydrogenation of benzene is much less than the heat of hydrogenation of three cyclohexenes3 and the known unwillingness of benzene to undergo addition reactions, opting for “aromatic” substitution instead. These data have prompted an on-going preoccupation with “resonance energies”, “aromaticity”, and the like. In this chapter, we suggest that, while the experimental facts are indisputable, the concepts which chemists have devised over more than a century are most likely erroneous and that benzene is pi destabilized but operationally “aromatic”.
KeywordsResonance Energy Configuration Wave Sigma Bond Interelectronic Repulsion Total Excitation Energy
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