David F. Larder
Division of Natural Sciences and Frank F. Kluge Division of Language and Literature Nofre Dome University Nelson, British Columbia, Canada
Alexander Mikhailovich Butlerov's Theory of Chemical Structure
Alexander Mikhailovich Butlerov's classic paper of 1861 ( I ) has not been fully appreciated by western historians of science primarily because it seems to lie outside the mainstream of contemporary thought, linlcing valency theory with modern structural theory through the establishment of bond formulas, and its importance has thus been underemphasized. Also, the German is very difficult and cumbersome, and this may have contributed to the poor reception accorded the paper when presented to the Speyer Congress on September 19, 1861. Butlerov attributed this lack of recognition to the provincialism of the Germans (#), though the language difficulty coupled with a lack of experimental data may well have been the major contributing factors. Russian historians have seen this paper as the foundation stone for structural theory, while Western historians have generally credited TCelcul6 and Couper with founding this theory. Why has this polarization between East and West come about and how can it be resolved? The translation of Butlerov's paper that follows seems to indicate only a small advance over the 1858 papers of Rekul6 and Couper. He defines chemical stvuctuve as "the nature and manner of the mutual binding of the atoms in a complex body," stating that "the chemical nature of a complex molecule is determined by the nature and quantity of its elementary constituents and by its chemical structure." This seems to state nothing very new since the primary change it introduces is that chemical properties arc more influenced by the nature and manner of the atomic binding than by the simple arrangement. Thus atr tention is focused on the binding between the atoms. The studies of Mitscherlich on isomorphism which became a mecl~anicalconsequence of the atomic construction of molecules, and the early nineteenth century crystallograpliic studies of Rome de I'Isle, Hauy, and Bravais, directed thought to the arrangement of the particles in matter and led t o the search for a deeper understanding of the inner constitution of molecules. The problem with the theory of atomic arrangements was that, until the decade of the 18501s,when valence theory was developing, there v a s no satisfactory way of determining how the atoms were arranged. True, there had been some suggestions from, among others, Dalton, Thomas Thomson, Wollaston, Ampdre, and Baudrimont; but these had been speculative and not well developed. However, in the classic papers of Couper and ICelcuI6 in 1858, as well as in a lecture given by Butlerov the same year, the radicals and types that had been current in organic chemistry for some twenty years were broken down into formulas in ~ h i c hthe atoms vere linked together according to the rules of
valence and the thesis that carbon atoms could be linked to each other. This development reinforced a gcometrical-mechanical-structural concept in which the dissection of the molecule into its atomic components led readily to the formulas of Couper and Crum Bro\vn, vhich are essentially modern formulas. However, the subsequent developments of structural theory have led to a reinterpretation of these primitive formulas througb the implicit inclusion of such concepts as tautomerism, resonance, induction, and steric hindrance. Thus, without essentidly changing the formulas from the lSGO's, a completely new interpretation of their meaning has been interpolated t,hrough the addition of empirical rules (9). Rykov has indicated (d), in considering Butlerov's scientific method, that Butlerov w\.as a dialectrical materialist. If Rutlerov's 1861 paper is viewed from this standpoint, we can immediately perceive the difference in thinking between Rutlerov, and his theory of chemical structure, and Couper and Ikkul6, and what is considered by Western historians of science as their structural theory. ilIaterialism considers mat,ter to be the universal substance and :I chemist normally thinks in materialistic terms. Tbe dialectical philosoph~places :L very different emphasis on the evaluation of problen~st,llan does tbe mechanical philosophy of a melaphysical approach. The dialectical method involves a realization of the essence of reality as a process of flux or change-a realization of the existing state of things and of its inevitable breaking up. There is not a causal relationship but a process of becoming. The dialectic involves the thesis, or afirmation of the existing state, the antithesis, or recognition of the negation of this state, the existing state's inevitable break up, and the synthesis between thesis and nv~titl~esis.Thus, in chemical structural terms, emplrasis is on the relstionship ("synthesis") bet~reenthe state of the r e d a n t molecule and that of the product molecule. The i\4arx-Engels dialectic accepts this from Hegel and adds an empirical dimension derived from lkurbach, though criticizing both Hegel and Veorbach for their emphasis on things rather than on processes. Againin chemico-structural terms, tbe process of conversion of reactant into product, rather than the reactant and product pel. se, should be emphasized. Hegel's central tbeme is the reconciliation of being and thought, but the post-Hegelians, including I~euerbacli,in the 1830's and 1840's reconciled thought with itself (6). The determinations that aRord real knowledge w e idways only those that determine the object by the object itself, rrnrnely, by its own individual determinations; thus, they are not general Volume
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determinations, as the logical metaphysical determinations are, which determine no object because they extend to dl objects without distinction.
Mechanism reduces complex phenomena to combinations of simple phenomena and views the complex from the viewpoint of the simple. This introduces a causal relationship which, in the present instance of molecular theory, involved the reduction of the radicals and types of molecules in the pre-1858 period into single atoms. This is the viewpoint of Couper who, following the Scottish Common Sense philosophy of Sir William Hamilton and the Reidian school, insisted on the necessity of analyzing the molecule into its atomic components and synthesizing these latter back into atomic molecular diagrams or formulas. Adding the concept of carbon-carbon linking in organic compounds to the established valence theory, and confining his attention to relatively simple compounds, he maintained that the whole is simply a derivative of its parts. IZelcul6 reached similar conclusions although his philosophical standpoint is less clearly defined than that of Couper. The Couper-Kekul6 theory mas presented at a time when chemists were struggling with the cumbersome radical formulas which enabled reaction types to be represented. In retrospect, it seems to be a natural development which enabled reactions to be followed in terms of formulas. Couper was particularly critical of Gerhardt's type theory and saw a causal relationship between the atoms and the molecule by the use of valence theory and the mutual linking of carbon atoms. For Butlerov then, the chemical properties of a compound are potentially present, and realized only by observations in the course of a chemical process. The whole molecule takes part in a reaction and gives rise to reaction taking place a t a particular part of the molecule. It is the chemical properties that are emphasized in this paper, though he recognizes the legitimacy of physical examination of the molecule in its static state. He emphasizes the dynamics of chemical change, contrasted mith the statics of physical observations leading to the mechanical arrangement of the atoms in the molecule. No such distinction is made by Couper or Rekul6 in 1858, nor by Crum Brown in 1861. Butlerov reinforces emphasis in his widely read "1,ehrbuch der organischen Chemie" (1868), translated from the earlier Russian edition of 1864, when he insists that the "chemical nature" is "the total chemical character of a compound." He also stat,es that (6)
. .. in
the chemical nature of every complex molecule cantaining atoms, an element is limited on the one hand by its nature and chemical arrangement in t,he molecule, and on the other, by the nature, amount and chemical arsngement of the remaining atoms in t,he same molecule.
The important distinction being made here is between the pbysico-mechanical structure of a molecule, and its chemical structure. The viewpoint in each case is very different. I n addition Butlerov points out his objections to the type formulas of Gerhardt, and emphasizes the increasing need to include atomicity (or valency) into a more modern theory of chemical stvucture. In tracing a line from the valency theory of the 1850's to moderu structural formulas we have become so used to interpolating an interpretation of the meaning of 288 / lournol of Chemical Education
modern formulas in terms of atomic interactions, steric hindrance, inductive effects, and so on that the contributions of Butlerov are neglected. All that seems necessary is to link together the earlier studies of Couper and IZekulB with the geometrical interpretations of van't Hoff to arrive readily a t modern formulas. Thus Butlerov's ideas are generally by-passed, and the geometrico-mechanical viewpoint associated with CouperKekulB-van't Hoff has been reinforced in the two philosophical studies by Benfey and Mulckhuyse (see General References). Butlerov does not neglect atomicity or affinity, but, places them in a supporting role to his ideas on chemical structure treated from this dialectical viewpoint. As Bykov has pointed out, valence and carbon-carbon linlcing are theses for Couper and I
