Copula theory

Soon thereafter, Kolbe s comrade-in-arms, Frankland, submitted for publication a landmark paper that, similar to Brodie s and Hofmann s work, pointed toward serious anomalies in the copula theory. As a master (indeed, the founder) of organometallic chemistry, Frankland adduced examples of reactions that indicated that tin, zinc, mercury, antimony, arsenic, phosphorus, and nitrogen exhibit fixed maximum combining capacities with other atoms or radicals. Arsenic and antimony, for instance, seem to combine only with three or with five equivalents of other atoms or radicals. If the maximum capacity is reached, then only substitution, not addition, of other components can occur. Frankland had turned he now allied himself with the ammonia type theory of Hofmann and Wurtz, for the semimetals antimony and arsenic seemed to follow exactly the pattern established by the new organic nitrogen compounds of the latter chemists. The theory of copulas, he declared, could no longer be maintained. ... 

The stated purpose of Kekule s polyatomic radical paper was to demolish the copula theory for good. Tarring Limpricht and Uslar with the same brush he was using on Mendius, he declared the copula theory to be complicated and unnecessary. Rejecting copulas was beneficial, for then all compounds could simply and clearly be represented as... 

Berzelius continued the attack on the theory of substitution. He proffered the copula theory, which proposed that chlorine caused a drastic rearrangement of the radical when it joined (copulated) with the hydrocarbon. This notion had no intuitive appeal because compounds did not show drastic differences in chemical properties, so this theory was generally rejected. Berzelius protested loudly, but few listened. Younger chemists, such as Auguste Laurent, were listening to Dumas. 

Berzelius had introduced his theory of copulae in order to reconcile his electrochemical theory of 1811 with the new phenomena obtained in the organic field which seemed incompatible with it. As time passed, the number of supporters of his theory diminished, and the number of its opponents increased. More and more complicated and improbable formulas became necessary to make the theory agree with experimental facts. Berzelius stratagem of regarding some compounds as conjugated compounds bore little resemblance to reality in many cases, and although Claus in... 

Berzelius introduced his theory of copulae to make his electrochemical theory (1811) compatible with newly discovered organic compounds, but with time the supporters of his theory were outnumbered by its opponents. Increasingly complicated and improbable formulas became necessary to reconcile the theory with experimental facts. In many cases, Berzelius device of regarding some compoimds as conjugated species bore little resemblance to reality. Claus (1854) and Blomstrand (1869) tried to revive and modify Berzelius ideas, but otherwise his theory was of little value. 

In his conjugate theory, which used terms and ideas corps copule borrowed from Gerhardt, Jons Jacob Berzelius (1779-1848) viewed metal-ammines as conjugated or copulated compounds consisting of ammonia and a conjugate or copula. The conjugate cannot be removed by reaction with an acid, and it neither decreases nor increases the saturation capacity of a base, that is, a metal conjugated with ammonia can still combine with other substances. 

Kolbe had been a student of Wohler and Bunsen, both Berzelians, but unlike them was passionately interested in chemical theory, especially the quest to determine molecular "constitutions" (identification of the particular radicals that combine to form a given molecule). He had imbued Frankland with the same passion, contrary to the positivistic tenor of the day. Kolbe and Frankland thought that this work strongly supported the Berzelian copula formulas in which they expressed their reactions. 

Berzelius s theory of copulae was introduced to save the electrochemical theory. Its supporters diminished, its opponents increased, and Berzelius s complicated and improbable formulae seemed to suggest that the radical theory had had its day. Bunsen s researches on cacodyl (see p. 283) seemed, indeed, to bring it new life, and in 1841 Berzelius said this is a triumphal chariot which has over-run and smashed the ramshackle barricades of Dumas. The theory of copulae was derided by the French school. Laurent said ... 

This was an important step, for two reasons (i) the older theory of radicals (as distinct from Gerhardt s residues) is fused with the type theory, and (2) attention is once more focused on the atoms as the real determining factor in chemical changes, instead of radicals or types. The vague idea of copulae also disappeared. 

Berzelius had thus tacitly accepted the fact of substitution and had attempted to incorporate it into his dualistic theory. He applied Gerhardt s terminology to radicals such as C2H6 and QCl, calling them copulae and referring to the compounds as copulated. This new stance by Berzelius won little support, and the dualistic theory was further undermined by an accumulating mass of evidence on the composition of acids. 

It is seen from this table. .. that the point of view of the formation of the series in the types can be applied to ethers as to bases, to radicals as to aldehyde, and to bases as to amides. Gerhardt thus applied his theory of residues (see p. 417) to radicals in types, obtaining conjugated (conjug6s) or copulated (copulas) radicals. The acids are derived from water by substituting radicals for hydrogen (as Williamson had done, see p. 450) ... 

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