Arenes and Aromaticity Special Introduction

That group of benzenoid hydrocarbons called arenes, already introduced in Chapter 3 and again in Chapter 5, might be thought of as compounds needing no further 

Subsequently, the problem was compounded by the isolation of additional materials, related to benzene (CeHe), from the fractionation of coal tar (vide supra). 

Hhe process of heating one or more of the varieties of coal to ca. 1000°C is called destructive distillation. The noncondensable gas is coal gas, the liquid condensate is coal tar, and the residue is coke, used for smelting iron in the steel industry. 

Albert Ladenburg (1842-1911) was a student of Kekule vide infra) who showed, by chemical reactions, the equivalence of the hydrogens of benzene. Ladenburg eventually became Professor at University of Breslau. 

The major difficulty of the diminished reactivity of benzene (CeHe) relative to that expected for alkenes alluded to earlier vide supra) could not be resolved by this (or any other equally inventive) suggestion. Indeed, until the tools of MO theory and experimental spectroscopy were integrated into the mainstream of organic chemistry, aromaticity was largely defined in terms of unexpected stability as measured by heats of hydrogenation -AH°, Chapter 3) and (with somewhat circular reasoning) by finding reactions that were characteristic of aromatic compounds vide infra). 

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