Radical Theory

Radical Theory

 

one of the leading chemical theories of the first half of the 19th century; it was based on A. L. Lavoisier’s concepts of the extreme importance of oxygen in chemistry and the dualistic composition of chemical compounds.

In 1789, Lavoisier, using the term “radical” (from the Latin radix, genitive radicis, “root” or “base”) that had been proposed in 1785 by L. B. Guyton de Morveau, expressed the opinion that inorganic acids are compounds of oxygen and simple radicals (radicals composed of a single element), whereas organic acids are compounds of oxygen and complex radicals (radicals composed of carbon and hydrogen). The discovery of cyanogen by J. L. Gay-Lussac (1815) and the similarity between the cyanides KCN, AgCN, and Hg(CN)2 and the chlorides KC1, AgCl, and HgCl2 (here and below, all formulas are given in modern notation) strengthened the concept of complex radicals as being groups of atoms that pass from one compound to another without undergoing any change. In 1819, J. Berzelius expressed his authoritative support of this concept.

In 1827 the French chemists J. Dumas and P. Boullay proposed that ethyl alcohol and ether be regarded as hydrates of “etherin” (ethylene) C2H4·H2O and 2C2H4·H2O. In 1832, J. von Liebig and F. Wöhler showed that the benzoyl atomic group, C7H5O, forms the compounds C7H5OH (benzoyl aldehyde), C7H5OCl (benzoyl chloride), and (C7H5O)2O (benzoyl anhydride). In 1834, Dumas and the French chemist E. Peligot introduced the name “methyl” for CH3 (methyl chloride, CH3Cl; methanol, CH3OH), and Liebig proposed the term “ethyl” for C2H5 (ethyl chloride, C2H5Cl; ethanol, C2H5OH). Liebig and Dumas believed (1837) that organic chemistry is the chemistry of complex radicals, and inorganic chemistry, the chemistry of simple radicals.

As a result of the great number of facts contradicting the radical theory, it was superseded in the period 1840–50 by the theory of types. Nevertheless, the radical theory played a progressive role as a means of classifying organic compounds and as one of the premises for the creation of the structural theory. (For a discussion of the current state of the teachings on complex radicals, see.)

S. A. POGODTN

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