Radical theory

Under the radical theory was understood one of Justus von Liebig, Friedrich Wöhler and Auguste Laurent in 1830 developed theory to the structure of organic compounds.

Auguste Laurent then used the term radical for ordinary and accessory nuclei from individual atoms or even groups of atoms in the core theory.

The term radical individual section the free radical theory is not to be equated with the modern concept of the radical in the current theoretical chemistry concepts. In the radical theory statements about the composition of a chemical the body are made ​​of these consists of several small groups of elements, just the radicals.

Together with the also developed by Justus von Liebig, new methods of elemental analysis was the theory pioneered the understanding of organic chemistry and its reactions in the 19th century.

Other considerations were about the same time in 1834, designed substitution theory (see History of the substitution reaction ) by Jean -Baptiste Dumas with the notion of substitutability of the hydrogen in organic compounds, for example by halogens.

Problem

In the study of many compounds, most of which were isolated from natural products, it was found that this very often consist of only three or four elements, namely carbon, hydrogen, oxygen and nitrogen rare. With the help of elemental analysis, the molecular formula of the substances could be determined, however, many substances were already known at that time, the same composition ( molecular formula ) had completely different properties. Thus, the chemical properties also hung on the link between the elements, the structure of a compound was not determined by the previous methods.

Moreover, it was believed at that time, be that in a chemical reaction, all substances participating separated into its components and re-assembled. But this contradicted the fact that the empirical formula of the substances in a reaction often changed only slightly and the findings from the already advanced inorganic chemistry could therefore not be applied.

Model the composition of radicals

Liebig and Wohler therefore developed a model in which they assumed that a substance of several smaller groups of elements, the so-called radicals, there, would have been assumed unchanged in the reaction. The term radical is, however, only be understood in terms of a group of atoms, since at times Liebigs the modern atomic models do not yet exist.

Clearly, the model can be compared with a finished house. If the owner of the house wants to have a bay window instead of a balcony, it makes no sense to tear down the entire house and rebuild along with the building fabric for a bay window. Instead, only the old balcony and knocked off the bay is rescheduled.

Experiments to confirm the theory

To confirm the theory studied Liebig and Wöhler the composition of benzoic acid, a drug which has been derived from the resin of an East Indian plant, but that could also be obtained if one could stand in the air bitter almond oil, a well known and popular fragrance. Today, the active compound from benzoic known as benzoic acid while the major constituent of oil of bitter almonds benzaldehyde. They found that distinguished the two structures in the sum formula in only one oxygen atom. In addition, they were able to produce another substance by chemical reactions, they called Benzoestoff (today benzyl alcohol), in which the hydrogen content was higher by two units as the bitter almond oil.

After the fundamental relationship of the three substances was proved, they performed various chemical reactions with the materials, including the reaction with chlorine, bromine, iodine and ammonia. They could show here that a basic framework with the formula C7H5O unit always remained untouched in the reactions. Liebig and Wohler called this basic framework benzoyl and regarded it as a radical of benzoic acid, which is surrounded by all other substances.

"We find that they are all grouped around a single connection, which does not change in almost all their union relationships with other bodies its nature and composition. This resistance, this consistency in the phenomena, prompted us to assume that combination as a composite commodity, and for a special designation, the name of benzoyl propose. "

Effects of free radical theory

The free radical theory can be regarded as one of the cornerstones of modern organic chemistry, because here for the first time the concept of subdivision of a molecule has been described in several functional units. This concept is still used today as part of the functional groups and is the basis of the division into classes of substances. The systematic nomenclature of compounds uses these subdivisions, said based on the benzaldehyde C7H5O unit the prefix benzoyl continues to receive.