MEETINGS AND CONFERENCES

CONFERENCE ON THE THEORY OF CHEMICAL STRUCTURE IN ORGANIC CHEMISTRY

In June 1951, the Division of Chemical Sciences of the Academy of Sciences of the USSR convened in Moscow a conference on the theory of chemical structure in organic chemistry. The work of the conference, which lasted four days, was attended by more than 400 chemists, as well as physicists and philosophers representing various scientific institutions and higher educational establishments of Moscow, Leningrad, Kiev, and other cities of the Soviet Union.

To prepare the main report at the conference, the Division of Chemical Sciences of the Academy of Sciences of the USSR created a Commission under the chairmanship of Academician A. N. Terenin, which included Corresponding Member of the Academy of Sciences of the USSR V. N. Kondrat’ev (deputy chairman), Corresponding Member of the Academy of Sciences of the USSR I. L. Knunyants, V. V. Korshak, M. I. Kabachnik (scientific secretary), and N. D. Sokolov.

The report presented by the Commission includes the following sections.

1. Butlerov’s doctrine and its role in the development of chemistry.
2. The development of structural theories in the second half of the nineteenth and the beginning of the twentieth century.
3. The achievements of Soviet organic chemistry.
4. Quantum chemistry and the theory of structure.
5. On the so-called “resonance theory.”
6. On the errors of certain Soviet scientists.
7. The present state of the Butlerov–Markovnikov doctrine on the mutual influence of atoms in a molecule and on reactivity.
8. Prospects for the further development of the theory of structure.

At the beginning of the report it is stated that the basic propositions of the theory of chemical structure, which is the foundation of chemistry, were developed by the brilliant Russian chemist Aleksandr Mikhailovich Butlerov. Over the 90 years that have passed since the creation of the theory of chemical structure up to the present day, the latter has invariably been and remains a guiding star in all investigations and applications of organic chemistry.

The concept of the chemical structure of a molecule includes all those characteristics which, in their totality, determine the chemical behavior (reactivity) of the given molecule. These include: the nature of the atoms forming the molecule, their valence state, the order and character of the bonds between them, their spatial arrangement, the character of the distribution of electron density, the character of the “polarizability” of the electron cloud of the molecule, and so on.

Butlerov himself defined the concept of chemical structure as follows: “Proceeding from the idea that every chemical atom entering into the composition of a body takes—

takes part in the formation of the latter and acts here with a definite quantity of the force belonging to it, the chemical force (affinity). I call chemical structure the distribution of the action of this force, as a result of which chemical atoms, mediately or immediately influencing one another, combine into a chemical particle.”

The basic propositions of Butlerov’s doctrine may be formulated as follows:

1) the molecule possesses a quite definite structure (the arrangement of atoms in space, the order or sequence of bonds);

2) the chemical properties of substances are directly dependent on the chemical structure of their molecules, and the latter can be known by chemical means;

3) for the chemical behavior and properties of a molecule, the mutual influence of the atoms in the molecule is of primary importance; Butlerov distinguished the mutual influence of atoms not directly bound to one another from that of atoms directly joined.

By pointing to the important role of the mutual influence of atoms, Butlerov thereby emphasized the significance of the circumstance that, in the formation of a molecule, new qualities appear that are not inherent in the individual atoms, but are characteristic precisely of the given aggregate of atoms joined in a quite definite manner.

In the course of its development, the theory of structure embraced all of organic chemistry and acquired an unsurpassed power of prediction, both with regard to establishing possible types of chemical compounds and numbers of isomers, and with regard to predicting the chemical properties of organic substances. Based on experience and firmly relying upon it, the theory of chemical structure is profoundly materialistic and correctly reflects the objectively existing laws of organic chemistry, dialectical in their nature.

Soon after Butlerov formulated the basic propositions of the theory of chemical structure, and this theory began to win ever greater recognition among foreign chemists, Butlerov’s name began to be mentioned less and less often when the ideas he had expressed were repeated. For bourgeois chemist-scholars, underestimation, omission, and distortion of Butlerov’s theory of structure and the suppression of Butlerov’s name became characteristic.

There is an obvious tendency to distort the true meaning of Butlerov’s theory of chemical structure, a tendentious falsification of historical facts, amounting to a belittling of the significance of Russian science.

The report speaks further of the inestimable contribution made to the development of the theory of chemical structure by Russian and Soviet organic chemists—Butlerov’s pupils and followers. The creation of the world’s first socialist state, which opened up boundless possibilities for the further development of science and industry, had an enormous influence on the development of organic chemistry. The brilliant development of research in the field of the synthesis of chemical compounds on the basis of the theory of structure, which led to the creation of a powerful industry of heavy organic synthesis and the production of complex organic preparations, gives grounds for speaking of the flourishing of theoretical and experimental chemistry in the Soviet country.

The development of the theory of chemical structure was substantially influenced by the successes of experimental and theoretical physics.

The report states that the application of quantum mechanics to problems of the chemical structure of molecules contributed to the further development

Butlerov’s doctrine. A special branch of theoretical chemistry arose—quantum chemistry—which became an integral constituent part of the theory of chemical structure.

Quantum chemistry developed by means of the theoretical treatment of regularities previously established in chemistry; moreover, the agreement of the conclusions of the theory with the data of chemistry served as confirmation of the correctness of the propositions of quantum chemistry, which had acquired the possibility of prediction. Quantum chemistry made it possible not only to give a deeper interpretation of concepts previously established in chemistry, but also to create new conceptions, and it also greatly contributed to elucidating the interrelation between the chemical and physical properties of molecules (and atoms). Quantum chemistry clarified the nature of the chemical bond, explained the capacity of chemical bonds for saturation, physically substantiated many important propositions of stereochemistry, and explained a number of other important features of molecular structure.

It is quite natural that the laws of quantum mechanics do not exhaust all the regularities to which the chemical form of motion of matter is subject. When we speak of the chemical form of motion, we have in view the processes of transformation of some substances into others, occurring as a result of the redistribution of bonds between atoms and the rearrangement of the electron shells of atoms and molecules. At the basis of the chemical form of motion of matter lie the quantum laws to which electrons, atoms, and molecules are subject. However, the specificity of the chemical form of motion is determined not only by these laws, but also by those regularities that are connected with the existence of complex forms of interaction among a large number of particles (electrons, atoms, molecules) and are not embraced by quantum mechanics. Such questions as the reactivity of substances, the mechanism and kinetics of their chemical transformations, cannot be studied with the aid of quantum mechanics alone and for their theoretical treatment require the involvement of statistical theories. Naturally, the theory of chemical processes must rely first of all on the study of these very processes; in other words, the study of the chemical form of motion of matter must always be based on chemical paths of investigation.

The quantum-mechanical theory of the chemical bond proceeds from new conceptions of the nature of the electron (wave properties, subordination to the Pauli principle). Quantum mechanics provides an equation for finding the wave functions and energies of both the ground and excited states of a molecule. However, owing to mathematical difficulties, it is impossible to solve the wave equation exactly even for a single molecule, and therefore one has to resort to various approximate methods.

The approximate quantum-mechanical calculation of the hydrogen molecule was historically the first step on the path of applying quantum mechanics to the problem of the chemical bond. This calculation had fundamental significance, since it served as the starting point for the quantum theory of the homopolar bond.

The quantum-mechanical calculation of the hydrogen molecule showed that, for the interaction of atoms (and molecules), of all the forces known in nature only electric forces are significant. At the same time, the quantum properties of electrons mentioned above play an essential role; without taking them into account it is impossible to understand the nature of the chemical bond and the chemical properties of atoms and molecules. The success of the calculation of the molecule \(H_2\), as well as of some other simplest molecules (\(H_2^+\), \(LiH\), \(Li_2\), etc.), confirmed the applicability of quantum mechanics to solving problems in the theory of the chemical bond.

In the Heitler and London method (the “electron-pair” method), the quantum properties of electrons are reflected in the expression for the energy of the molecule,

in particular, in the form of the so-called exchange integral. In connection with this term, one sometimes encounters, as a result of its incorrect interpretation, the notion of electronic “exchange” and of special “exchange forces” supposedly existing in the molecule and determining its stability. In reality, however, there are no grounds whatever for assertions about the existence of special “exchange forces” or “exchange” of electrons as a phenomenon responsible for the chemical bond.

By means of quantum-mechanical calculations of the simplest molecules, a physical interpretation has been obtained for the concepts of valence and the covalent bond; the factors determining the valence of various atoms have been clarified more fully; the nature of the repulsion of closed electron shells has been elucidated, as well as the nature of the saturation of chemical bonds and of the energies of chemical reactions; the nature and special features of multiple bonds have been clarified to a considerable degree. Quantum-chemical calculations have made it possible to give a physical foundation to many important propositions of stereochemistry. An approximate theory of directed valences was created, explaining the geometrical configuration of many molecules.

Quantum-mechanical calculations of many-atom molecules, carried out by the methods of “electron pairs” and “molecular orbitals,” are extremely approximate and may be regarded only as essentially semi-empirical. The quantitative results obtained with their aid cannot, without additional investigation, be considered substantiated and reliable. However, these calculations often lead to general qualitative conclusions that appear sufficiently well founded, provided that they are not connected with the particular character of the assumptions underlying the method of calculation employed. These general qualitative conclusions have made it possible to interpret a number of features of complex molecules.

Thus, from the indicated calculations it followed that the idea developed earlier by chemists of the possibility of transmitting the mutual influence of atoms not directly connected in a molecule along a chain of bonds by means of redistribution of its electron density is in complete agreement with the quantum properties of electrons. Quantum chemistry contributed to the discovery of those specific laws to which these changes in the distribution of electron density are subject. It was shown, for example, that the interaction of two adjacent parts of a molecule and, consequently, the influence of one of its parts on another, is considerably weakened as the axes of the $\pi$-clouds of two directly bonded atoms deviate from parallelism. This prediction of quantum chemistry was subsequently confirmed experimentally.

For molecules with a system of conjugated double bonds*) a very simple model was proposed, according to which all $\pi$-electrons of the molecule move in a potential box whose length is equal to the length of the chain of conjugated bonds. Such a model describes well the spectroscopic regularities of certain molecules of this type and confirms the fact, known in physics and chemistry, that in molecules with conjugated $\pi$-bonds the mutual influence of atoms can be transmitted without attenuation over considerable distances.

Thus, thanks to the successful application of quantum mechanics to the development of the problem of the chemical bond and of the structure of molecules, many propositions of the theory of chemical structure received a physical foundation, and new ideas were created which play an important role in the development of the theory of chemical structure.

*) The structure of molecules with conjugated double bonds is represented, as is well known, by formulas of the type —C=C—C=C—C=C— (for example, butadiene, hexatriene, etc.).

MEETINGS AND CONFERENCES

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In evaluating the significance of quantum mechanics for chemistry, one should draw a clear line between the true results to which quantum chemistry leads and the erroneous interpretation of certain approximate quantum-mechanical calculations from which there arose the so-called concept of “resonance.” This concept, developed chiefly by foreign scientists (Pauling, Wheland, and others) and widely current abroad, speculated on principles of quantum mechanics that in no way followed from their essence; the concept of “resonance” in fact came to claim the role of a general theory of chemical structure.

The content of this concept comes down to the assertion that in molecules there supposedly exists a special quantum-mechanical phenomenon—“structural resonance,” which consists in the “superposition” upon one another of separate, supposedly objectively existing “states” (“structures”); this “superposition” (“resonance”) stabilizes the molecule and determines all its most important properties and even its very existence.

The term “quantum-mechanical resonance” was borrowed by Pauling from one of Heisenberg’s early works, in which the helium atom was calculated. As is known, in this work a formal analogy is drawn between a system of two electrons and a system of two identical, weakly coupled pendulums.

However, this analogy is limited to the formal similarity of certain mathematical equations solved in the calculation of these systems, and exists only so long as the calculation of the electronic system is carried out in the zero approximation by means of this method. This method, in a somewhat modified form, was later used by Heitler and London for the calculation of the hydrogen molecule, and subsequently it was extended to many-electron molecules and is known under the name of the method of “electron pairs” or “valence structures.” If, for the calculation of a many-electron system, one uses other methods, then the indicated analogy with the problem of small mechanical oscillations generally does not arise.

When using the method of “electron pairs,” one proceeds, as is known, from one-electron functions of separate atoms, and the desired wave function is represented as a sum of several terms $\varphi_i$, each of which corresponds to a definite distribution of spins between atoms. To facilitate the calculation, each of these terms is depicted by a corresponding “valence scheme,” and the number of terms is determined by Rumer’s theorem. Pauling calls these “valence schemes” “resonance structures.”

It is quite evident that none of these terms of the wave function, taken separately, determines any real state of the molecule.

In fact, the individual terms $\varphi_i$ in the superposition have a real physical meaning only in the case where such conditions can be created under which the given system (molecule) proves to be in a state with the proper function $\varphi_i$, and at the same time will not be destroyed. Obviously, the functions $\varphi_i$, corresponding to individual valence schemes and not representing any proper functions of the problem under consideration, do not satisfy this requirement. Only linear combinations of these functions can correspond to real states of the molecule.

The circumstance that, in calculating a molecule, it is necessary in the general case to take into account all valence schemes also served as the basis for the assertion that in molecules there exists “quantum-mechanical resonance of structures.” Thus, the peculiarity of one of the approximate—

...of the calculation methods was falsely interpreted as the expression of a certain objective reality. It is clear that neither the phenomena of “resonance” nor “resonance structures” in molecules actually exist.

Moreover, the individual terms of the wave function, represented in the form of valence schemes, are not connected in any way characteristic of each of them with the experimentally observed quantities that characterize the molecule under consideration. It follows from this that no information about the molecule can be extracted from these terms—still less from their graphic representations—beyond that which served as the guide in constructing them.

It is not surprising that this “theory” has proved practically fruitless. By developing their concept, Pauling and his supporters systematically began to present “resonance structures” and their “resonance” as something primary, objectively existing in the molecule, predetermining almost all of its properties. Thus they replaced the real factors determining the properties of the molecule by imaginary images, fictitious concepts, and distorted the true meaning of the results of applying quantum mechanics to problems of molecular structure.

Chemical literature became flooded with speculations claiming to explain observed facts. In reality, however, the concept of “resonance” could explain nothing, since its supporters understood explanation to mean a reference either to “resonance” or to particular “resonance structures” torn away from experiment. The abundance of conceivable “resonance structures” which the concept of “resonance” placed in the hands of the chemist—especially with the introduction of the so-called “ionic structures”—made it possible only to create the harmful illusion of an explanation where in essence no explanation was given.

The “theory of resonance,” operating with valence schemes that have no connection with experiment, mistakenly identified them with structural formulas and thereby transformed the latter from a means of representing the molecule into something primary, standing above the molecule and predetermining its properties. The principal aim of the “theory” was proclaimed to be the reduction of the whole diversity of molecular properties to “combinations” of certain arbitrarily chosen “resonance structures.” Such a departure into the realm of speculative conjectures and the substitution of fictions for real relations characterize the “theory of resonance” as an idealistic conception.

Pauling’s student, Wheland, acknowledges that the “idea of resonance” is a “speculative conception” and “does not reflect any intrinsic property of the molecule itself.” This does not prevent him, a few lines below, from raising the question of the “influence of resonance” (i.e., of a speculative conception!) “on the physical and chemical properties of molecules.” Wheland tried to justify his obvious inconsistency by asserting that this conception is “convenient.” From such statements it is evident that the supporters of the “resonance” conception stand on Machist positions. For them it is immaterial that their theory does not reflect objective reality; for them any “theory” is acceptable if, in their opinion, it is “convenient.”

In essence, the “theory of mesomerism” of the English chemist-organicist Ingold coincides with Pauling’s concept of “resonance.”

The chemist had long ago come to the conclusion that, using the usual arsenal of representational means (valence strokes, plus and minus signs), it is impossible correctly to depict by means of a single formula the electronic structure of certain molecules. Thus, for example, in the simplest case of the benzene molecule, in order to convey the symmetry in the distribution of electron...

one has to write two ordinary structural formulas:

The simultaneous use of two (or several) such formulas is regarded as a comparison of the given molecule with other molecules related to it in structure, differing (in the case being compared) only in the distribution of electron density. In doing so, one abstracts from certain secondary features of those real molecules with which the comparison is made, and in the formulas only the essential is reflected. Thus, each of the benzene formulas given above is constructed from “vinylene” groups —HC=CH—, which enter into the composition of various unsaturated compounds. In this way, these formulas essentially represent scientific abstractions, and the mode of representation is a method of comparison well known in chemistry and one that has fully justified itself. The true electronic structure of a molecule is not conveyed by any one of these formulas, but in reality is more or less intermediate with respect to them. Knowing the properties of the compounds to which these formulas appeal, one can make certain predictions about the properties of the compound under consideration.

Often, instead of depicting a molecule simultaneously by several structural formulas, one of them is used, supplied with curved arrows indicating the difference of the true distribution of electron density in the molecule from the distribution depicted by the given formula. Thus, the benzene molecule could be represented in the following way:

With such an interpretation, there is, of course, nothing vicious in the use of several structural formulas or of one formula supplied with arrows. On the contrary, such a method, like the use of any scientific abstraction, makes it possible to understand more deeply the structure, the mutual relations and connections of various substances with one another, to reveal general regularities, and so forth.

However, Ingold, in using two or several structural formulas to depict certain molecules, quite erroneously began to treat them as though they were all contained in the given molecule, and, following Pauling, began to assert that the superposition (“resonance”) of these “structures” stabilizes the molecule and predetermines its properties. In other words, Ingold’s theory of “mesomerism” is indistinguishable from Pauling’s concept of “resonance” and is therefore just as vicious as the latter.

From all that has been set forth it is quite clear that the “theory of resonance” (“mesomerism”) is idealistic, contradicting all the data of modern science. It is methodologically vicious, physically untenable, and fruitless. The concept of “resonance” has caused considerable harm to the development of the doctrine of chemical structure by diverting many researchers toward fruitless and useless pseudoscientific

constructed and created a harmful illusion of explanation for observed facts that remained in fact unexplained.

As indicated in the report, this conclusion is in no way refuted by the fact that a number of important results that have entered modern organic chemistry were initially formulated in the language of this conception.

The report also emphasizes that the criticism of the conception of “resonance” does not affect the essence of quantum-mechanical methods for calculating molecules, but concerns only their erroneous interpretation and the speculative constructions arising therefrom.

The conception of “resonance” has long been criticized by Soviet scholars. Among the first critical statements were those of Academician N. D. Zelinskii, who, already at an early stage in the development of the “theory of resonance,” repeatedly publicly noted the untenability and fruitlessness of this conception.

Recently the conception of “resonance” has been subjected to devastating criticism in a number of articles by Soviet scholars, as well as in broad discussions held in a number of scientific institutions and higher educational establishments. In these articles and discussions, deserved criticism was also directed at certain Soviet scholars who were uncritical in their attitude toward reactionary trends in Western European and American chemical science and who acted as propagandists of the “theory of resonance.”

As indicated in the report, this applies above all to Corresponding Member of the Academy of Sciences of the USSR Ya. K. Syrkin and Doctor of Chemical Sciences M. E. Dyatkina, who bear the principal blame for the dissemination of the “theory of resonance” in our country. Being specifically engaged in quantum chemistry, Ya. K. Syrkin and M. E. Dyatkina not only failed to expose the false character and ideological viciousness of the “theory of resonance,” but, on the contrary, widely popularized this conception and, in a number of cases, by developing it, aggravated the errors of Pauling and Wheland. Their propaganda of the “theory of resonance” was combined with an inadmissibly contemptuous attitude toward the works of Russian chemists and physicists and with deference to foreign “authorities.” In the book by Ya. K. Syrkin and M. E. Dyatkina devoted to the structure of the molecule, the name of A. M. Butlerov is not mentioned even once, and the meaning of his theory of valence is presented in a distorted form.

The report also points to errors contained in the books of Acting Member of the Academy of Sciences of the Ukrainian SSR A. I. Kiprianov, Prof. M. V. Vol’kenshtein, and also in articles and monographs by certain other Soviet scholars—organic chemists and physical chemists.

The report also notes the errors committed by Prof. G. V. Chelintsev in connection with his criticism of the conception of “resonance.” His repeated critical statements have to a considerable extent drawn the attention of the Soviet scientific community to this question; however, the criticism of the “theory of resonance” has been and is being conducted by G. V. Chelintsev from the standpoint of the “new structural theory” advanced by him, which is opposed by him to all modern theory of chemical structure and contradicts experimental facts and the foundations of quantum physics. At the basis of Chelintsev’s theory lies the postulate according to which, in a molecule, “each electron orbit is localized in one or two atoms.” From this position he attempts to explain all chemical regularities and facts. For this purpose he has to resort to ever newer speculative postulates, but even these do not remove the contradictions of his theory with the facts. The report indicates that Prof. G. V. Chelintsev’s “new structural theory” has no scientific foundation and must be rejected.

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The most extensive section of the report is devoted to the present state of Butlerov’s and Markovnikov’s teaching on the mutual influence of atoms in molecules and on reactivity. This section deals with the electronic interpretation of the nature of the mutual influence of atoms in molecules, created and successfully developed on the basis of the ideas of Butlerov and Markovnikov.

This interpretation is based on the proposition that the chemical properties of a molecule depend on the structure of its outer electron shell. As a first approximation, the electron shell may be characterized by the distribution of the density of its charge and by its ability to redistribute itself (“deformation”) under the influence of various factors, in particular during the process of reaction. The approximate nature of such a characterization is due, in particular, to the fact that with such an approach the quantum properties of electrons cannot be taken sufficiently fully into account. Nevertheless, the use even of these approximate conceptions has made it possible to draw important generalizations, explain many known regularities, found experimentally, and predict new facts.

The modern electronic interpretation of the mutual influence of atoms in a molecule distinguishes two principal effects: the inductive effect and the conjugation effect, and both can manifest themselves both in the equilibrium state and at the moment of reaction. Both effects consist in the fact that, when a new substituent is introduced into the molecule and with other structural changes, the distribution of electron density in the molecule changes, not only in the immediate vicinity of the center of disturbance, but also in other parts of the molecule, which entails a change in its properties.

The inductive effect is observed in molecules having only σ-bonds or isolated multiple bonds. It is characterized by rapid attenuation with distance, caused by the weak interaction of the bonds. For example, the replacement of a hydrogen atom in the molecule of acetic acid by a chlorine atom causes an inductive displacement of electron density, propagating along the chain of atoms in the molecule indicated by arrows,

\[ \mathrm{Cl} \leftarrow \mathrm{CH}_2 \leftarrow \mathrm{C}\!\left(=\mathrm{O}\right) \leftarrow \mathrm{O} \leftarrow \mathrm{H}, \]

which is manifested in the easier ionization of the O—H bond, i.e. in an increase in the acid dissociation constant. As the chain length of the molecule of a carboxylic acid increases, the change in the dissociation constant upon replacement of a hydrogen atom by a chlorine atom at the carbon atom most distant from the OH bond rapidly decreases.

The conjugation effect is observed in molecules having a system of conjugated double bonds, and in aromatic molecules. In contrast to the inductive effect, the conjugation effect transmits the mutual influence of atoms over considerable distances almost without attenuation. Thus, for example, the specific reactivity of the methyl group of an acetic ester

\[ \mathrm{CH}_3-\mathrm{C}\!\left(=\mathrm{O}\right)-\mathrm{OR}, \]

caused by displacement of the electron cloud toward oxygen (which is indicated by the curved arrow), retains its properties also in the case when it is separated from the COOR group by a chain of conjugated bonds,

as in crotonic and sorbic esters:

\[ \mathrm{CH_3-CH=CH-C\!\left(\begin{array}{c} =O\\[-2pt] \backslash OR \end{array}\right)} \]

\[ \mathrm{CH_3-CH=CH-CH=CH-C\!\left(\begin{array}{c} =O\\[-2pt] \backslash OR \end{array}\right)} \]

The conjugation effect has a number of other features, which are reflected both in the chemical and in the physical properties of molecules.

In the development of the basic propositions of the theory of chemical structure concerning the connection between the reactivity of substances and their chemical structure, a conception was elaborated in organic chemistry of the ionic and radical course of chemical reactions. The reaction of each of these types may have different mechanisms: it may proceed either with preliminary dissociation, respectively, into ions or radicals, or without such dissociation—through an activated complex. In connection with the discovery of radical reactions in solutions, the concept of chain reactions was successfully applied in organic chemistry; the theory of such reactions for the case of the gas phase had been created in the Soviet Union.

The report notes that the quantum-mechanical interpretation of the elementary act of chemical reactions has hardly even been outlined. A general theory that would make it possible, even qualitatively, to predict the rate of a chemical transformation and, in particular, to take into account the role of the medium, is at present lacking. Nevertheless, the existing ideas correctly reflect important aspects of objective reality and play a progressive role in the development of the theory of chemical structure.

The last section of the report is devoted to the prospects for further development of the theory of molecular structure. It points out, in particular, that the efforts of Soviet scientists should be concentrated on solving the chief, key problems of the theory of chemical structure. These include, first of all, deepening and expanding our knowledge of the chemical structure of substances, creating a theory of the mutual influence of atoms in the molecule, developing the problem of the dependence of the reactivity of molecules on their structure and on the medium in which the reaction proceeds, elaborating the problem of elementary processes in chemical reactions, establishing the dependence of various properties of substances—especially practically important properties—on chemical structure, and other tasks.

In conclusion, the chemical and physical methods that should be used to solve the tasks at hand are enumerated; in particular, the important role of the methods of quantum chemistry is indicated.

At the opening of the meeting, the chairman of the assembly, Academician-Secretary of the Division of Chemical Sciences of the Academy of Sciences of the USSR, M. M. Dubinin, delivered a brief speech. Recalling I. V. Stalin’s statement on the necessity of struggle of opinions and freedom of criticism for the development and flourishing of science, Academician Dubinin emphasized that this statement applies fully to the theory of chemical structure in organic chemistry, and called upon the meeting to engage in an active critical discussion of all the propositions put forward in the report, as well as of other questions of the present state of the theory of structure.

After the report by the chairman of the Commission, Academician A. N. Terenin, lively debates began. The overwhelming majority of speakers considered that the Commission’s report should in the main be approved.

The first to take the floor was Academician B. A. Kazanskii, who in his speech dwelt in detail on Butlerov’s teaching and its significance for organic chemistry.

Corresponding Member of the Academy of Sciences of the USSR B. A. Arbuzov, in his speech, pointed out that the main direction in the development of organic chemistry is organic synthesis in the broad sense of the word, as well as the study of the conditions under which reactions proceed.

Professor G. V. Chelintsev spoke with sharp criticism of the report. He said that the present conference must lead chemical theory out of the dead end into which it had been driven by idealistically minded bourgeois physicists and chemists. But, in his opinion, the matter was not helped by the fact that both the organization of the present conference and the keynote report were in the hands of former direct domestic supporters of the false theories of Ingold and Pauling. “Since the present conference must resolve methodological questions of chemical science, the keynote report should have given a clear opposition between the two historically formed and mutually exclusive solutions to the most important problem of chemical science—the structural problem.” This is absent from the report, and therefore it is “unquestionably untenable.” By the two mutually exclusive solutions to the indicated problem, Chelintsev understood, on the one hand, the interpretation of molecular structure set forth in the report, which in its physical aspect rests on quantum mechanics, and, on the other, his own “new structural theory,” based on the postulate of the “localization of electrons in one- or two-atom orbits” and other equally speculative postulates that contradict facts, quantum mechanics, and simple common sense. At the same time Professor Chelintsev in fact subordinated the question of the structure of a molecule to questions concerning the manner of writing structural formulas. As to the criticism of his theory given in the report, he was essentially unable to answer a single point. It is not surprising that Prof. Chelintsev’s speech found no support in the audience.

Professor M. M. Shemyakin criticizes, in particular, a recent speech in the press by M. I. Batuev,* who asserts that “chemists assign an obviously unfit means of investigating the structure of molecules to mathematics.” The speaker gives a very vivid example illustrating how modern ideas about the mechanism of the mutual influence of atoms in a molecule helped to predict the existence and to investigate the properties of new substances (propollonones), which proved to be practically very important.

Corresponding Member of the Academy of Sciences of the USSR A. D. Petrov says that the report is guilty of an excessive fascination with electronic concepts. In the speaker’s opinion, the primary task of chemists is the search for new reactions and the systematic synthesis of new substances, while the development of theory is a secondary task.

Corresponding Member of the Academy of Sciences of the USSR Ya. K. Syrkin, in his speech, acknowledged the “justice” of the criticism to which his works had been subjected in the report. He acknowledged that he had underestimated Butlerov, had mistakenly taken “resonance structures” for objective reality, and had used them to “explain” the properties of molecules. “It appears to me,” said Ya. K. Syrkin, “that a considerable share of the blame lies in the fact that these ideas were adopted in a number of books by many Soviet authors...” The speaker then gave a number of examples from which it is evident that the ideas set forth in the seventh section of the report are insufficient for explaining many facts. Touching on the prospects of quantum chemistry, Ya. K. Syrkin said that he evaluates them “rather pessimistically”; “today,” in the speaker’s opinion, “there is no suitable approach to such a solution that would give a sufficiently satisfactory approximation,” and “it is unlikely that anything can be done here in the near future.”

* “Questions of Philosophy,” No. 2, 1951.

Professor M. I. Usanovich says that, up to the present, in the field of structural theory there is no clarity in definitions. For example, there is no common opinion even on such, it would seem, a simple question as what valence nitrogen possesses in the ion $\mathrm{NH}_4^+$.

Professor V. K. Semenchenko notes that caution is necessary in using the apparatus of quantum mechanics. Quantum mechanics is made up of two parts—the mathematical apparatus, which undoubtedly reflects real reality, and conclusions, interpretations. In the speaker’s opinion, all physical and chemical theories must satisfy a requirement that he calls “physical or logical invariance.” If a concept worked out in an approximate theory, when transferred to a more exact theory, completely preserves its meaning, then it is “physically invariant”; it somehow reflects real reality and has a certain theoretical-cognitive value. From the speaker’s point of view, for example, the concept of a rigid molecular diameter, as not satisfying the requirement of “physical invariance,” has no theoretical-cognitive value. Likewise, the concepts of “exchange forces,” “resonance,” etc., do not satisfy this requirement. Answering questions, Prof. Semenchenko began to assert that on the same basis, when solving problems by the Heitler–London method, “even if you obtain exact numbers, these exact numbers do not make it possible to draw any theoretical-cognitive conclusions.”

Corresponding Member of the USSR Academy of Sciences S. N. Danilov points out that the report of the Commission is an important document. However, the speaker notes, many important questions are not represented in it. There are effects that cannot be reduced only to the motion of electrons.

M. I. Batuev, in his speech, accused the compilers of the report of the fact that it does not fully reveal the viciousness of the theory of resonance, for, in particular, it recognizes the lawfulness of the existing quantum-mechanical methods for calculating molecules, whereas in reality they are Machist. On this basis the speaker believes that the report must not be approved under any circumstances. Answering the question posed as to what, for example, the Machism of the molecular-orbital method consists in, M. I. Batuev replied that “the mathematical calculations are impermissible, including the electron-pair method, which immediately and directly lead to the energy of exchange forces (to the energy of resonance), as Prof. V. K. Semenchenko described very well yesterday.”

Corresponding Member of the Academy of Sciences of the Ukrainian SSR E. A. Shilov says that dynamic questions (i.e., questions of chemical transformations) cannot in principle be subordinated to the theory of the structure of organic compounds, for the theory of structure and the theory of transformation are two different theories. The shortcoming of such a formulation, which is also contained in the report, consists in the fact that it has led and continues to lead to attempts to find explanations of the chemical properties of organic compounds in one or another valence state of the nonreacting molecule, which is erroneous. The speaker gives numerous examples illustrating his assertion.

Docent O. A. Reutov discusses in detail the role of abstraction in chemistry and shows that the formulas used in chemistry are not fictions, as, for example, Prof. Chelintsev asserts, but scientific abstractions having great cognitive value.

Corresponding Member of the USSR Academy of Sciences I. L. Knunyants gives numerous interesting examples of the mutual influence of atoms in a molecule, drawn from his own research, and also discusses the untenability and contradictions of G. V. Chelintsev’s “new structural theory.”

Professor M. V. Vol’kenshtein admits that the interpretation of molecular structure from the point of view of resonance theory, once allowed by him, is completely erroneous. The speaker states that he has renounced the theory of re-

of resonance as early as 1941, but in his literary work has not been able consistently to carry out his point of view and not only has failed to show the falsity of the resonance theory, but has even continued to use its terminology.* M. V. Vol'kenshtein notes the extreme crudity of the existing methods for calculating many-atom molecules and points out that here there are serious physical and mathematical disorders. The speaker even sharply criticizes G. V. Chelintsev and M. I. Batuev, indicating that the latter in fact completely reject quantum-mechanical calculations. Having marked the directions in which, in his opinion, physicists should further develop Butlerov’s teaching, Prof. Vol'kenshtein, like the majority of the other speakers, expresses his approval of the report.

Professor P. G. Sergeev speaks of the necessity and difficulty of creating Soviet textbooks of organic chemistry.

The audience listened with great attention to the speech of Doctor of Physical and Mathematical Sciences E. I. Adirovich. He said that the danger threatening Soviet chemistry from the resonance theory has been eliminated. The resonance theory is not a consequence of quantum mechanics. Those who did not understand this at one time tried to declare that, since the resonance theory is the same quantum mechanics, “do not dare touch the resonance theory!”

Now, proceeding from the same erroneous premise, some people draw the conclusion: having rejected the resonance theory, quantum mechanics must also be rejected. The speeches of Syrkin and Vol'kenshtein are imbued with a very unpleasant pessimism in regard to it; there is supposedly no hope for the progressive development of quantum mechanics in its application to chemistry. The impression remains that, if the resonance theory has been abandoned, then quantum mechanics can no longer give anything to chemistry. This is an erroneous and harmful conclusion. The speeches of Chelintsev and Batuev in fact lead to the same thing: quantum mechanics must be removed from chemistry. Further, the speaker notes that quantum mechanics—the basis of our knowledge of the microworld—indicates that it does not fully describe transformation processes already because it is insufficient for this to consider an individual molecule; in any case it is necessary to consider at least the processes of energy removal in a reaction. Replying to M. I. Batuev, who called for considering the molecule only as a single dynamic whole, the speaker said that one must not separate the properties of the molecule from the properties of the atoms composing it, but show how they are connected with one another. In calling for the abandonment of existing methods and proposing no new, better ones, Batuev does not promote but hinders the development of science. The speaker pointed out that the Heitler–London method, as a method reflecting objective reality, cannot be considered idealistic. “Idealism in physics and chemistry rests not on quantum mechanics and not on quantum-mechanical calculations, but on the scientific and philosophical distortions of them. The resonance theory serves as an example of this.” Further, Prof. Adirovich noted that he does not share the pessimistic opinion that the problem of the many-atom molecule cannot be solved.

Corresponding Member of the Academy of Sciences of the USSR A. A. Maksimov considers that the report correctly assesses the state of affairs in its fundamentals and correctly indicates the prospects for the further development of organic chemistry. A. A. Maksimov does not agree with Prof. Chelintsev that the authors of the report are, in Chelintsev’s expression, a group of “Paulingists–Ingoldists” who have set themselves

* In January 1949, in UFN (Vol. XXXVII, issue 1), an erroneous review by M. V. Vol'kenshtein of the translation of Wheland’s book was published; in this review a confused interpretation was given of “resonance theory” as “the transitory hypothesis of chemical hypotheses,” and the work of Prof. Ya. K. Syrkin and his school on resonance theory was sympathetically assessed. (Ed. note)

task of repainting his “resonance façade” in a new color. One should not follow Chelintsev, who demands that the listed comrades’ reports be rejected and condemned. Pointing to the existence of a close connection between methodological distortions in questions of chemical theory and distortions in biology and physiology, A. A. Maksimov said that “the difference between the situation in chemical science and the situation in biology is that the Weismannist-Morganists were characterized by fruitlessness with respect to the practice of our construction, not to mention the harm they cause to the people. But will Prof. Chelintsev’s tongue turn to assert that ‘the Paulingists-Ingoldists’… have in the mass given nothing for the practice of construction?” A. A. Maksimov proposes abandoning such an insulting designation of Soviet chemists. The speaker goes on to say that physicists not only have not placed in their journals articles criticizing the theory of resonance, but here, at the conference, have not supported chemists in their struggle for advanced Soviet chemical science. Physics is, to a far greater degree than chemistry, littered with idealistic rubbish, which hampers the development of physics and related fields. A. A. Maksimov considers it necessary to note in the resolutions of the conference the abnormality of the physicists’ evasion of the struggle for advanced science in connection with discussion of the state of the theory of chemical structure.

In his speech Prof. M. G. Gonikberg says that in the development of the theory of organic chemistry there is a certain lag behind the development of the practice of Soviet organic chemistry. He sees four reasons for this lag: 1) the enthusiasm of some scientists for resonance theory (mesomerism); 2) the underestimation by some chemists of the importance of an in-depth study of the contemporary theory of chemical structure; 3) the weak connection of organic chemists with physical chemists and physicists; and 4) the absence of open discussions on questions of theoretical chemistry. Replying to M. I. Batuev’s speech, the speaker defends his accusations against quantum-mechanical calculations of idealism and viciousness. Prof. Gonikberg further expresses surprise as to why Professor Semenchenko needed to devise a new criterion of the truth of one or another theory. There is only one such criterion—practice.

Doctor of Chemical Sciences M. I. Kabachnik, noting that the criticism, given in the report, of certain Soviet scientists who failed to discern the viciousness of the “resonance theory” also concerns himself, says that work on the methodological analysis of the basic propositions of chemical science has in essence only just begun and must continue. The speaker indicates that Chelintsev, Batuev, and Meshcheryakov, in their speeches, “slander Soviet chemical science,” for in essence they deny the existence of a Soviet theoretical school in organic chemistry. However, contrary to the assertions of these comrades, such a school exists, although it has had some errors. M. I. Kabachnik further dwells on the question of what is abstract and fictitious as applied to the writing of chemical formulas. He emphasizes that the use of abstracted limiting formulas is a legitimate method of scientific analysis, making it possible to reveal the mutual influence of atoms in a molecule and the mutual relations of the molecules of various substances. In the conclusion of his speech the speaker convincingly demonstrates the untenability of Prof. Chelintsev’s “new structural theory.”

Doctor of Chemical Sciences M. E. Dyatkina says that the errors she committed were of two categories: 1) underestimation of the role of Russian science in the creation and development of theoretical chemistry and, chiefly, underestimation of Butlerov; 2) there was no clear understanding of what the “resonance theory” is. Having made an analysis of her errors, the speaker points out that for the successful development of quantum chemistry it is necessary to develop new methods of calculation, in particular, the use of machine technology.

Prof. B. M. Kedrov says that the gnoseological roots of the theory of resonance are mechanism, which, like every metaphy-

...physics, is a gnoseological source of idealism. Contemporary mechanism in physics is the striving to reduce all phenomena of nature (and society) to quantum mechanics. For a mechanist it is important to declare that in principle the higher—social life—is reducible to the lower. The resonance theory arose “out of the need of reactionary ideology to realize the concluding link in the general chain, which includes social Darwinism, Malthusianism, Vikhrovianism, Weismannism-Morganism, ‘physical’ idealism...” In criticizing the resonance theory, the speaker considers it important to show not only its erroneousness, but also the negative role that it objectively played. In this respect he was not satisfied with the speeches of Ya. K. Syrkin and M. E. Dyatkina. Answering a question put to him, Prof. Kedrov notes that “in Chelintsev’s theory there is an interesting positive thought,” according to which, “if an electronic model is created in chemistry, then it should not be made such that it would possibly include more fully all the data of physics.” In the speaker’s opinion, the attempt to do this “only unnecessarily complicates the question, makes its solution as applied to chemistry more difficult.” Answering another question, Prof. Kedrov states that “I consider the superposition principle in the formulation given by Dirac—its author—to be just as idealistic as the complementarity principle of Heisenberg, and considerably more idealistic than Pauling’s resonance theory.”

Corresponding Member of the Academy of Sciences of the Ukrainian SSR S. S. Urazovsky devoted his speech to the question of “cooperative transformations,” i.e., to the question of the influence of the medium on chemical processes.

V. M. Tatevsky notes that in the seventh section of the report it is not stated with sufficient clarity what mutual influence of which atoms is meant: atoms connected directly or by means of other, intermediate ones. He considers the depiction of a molecule by means of several structural formulas unacceptable.

Prof. B. A. Porai-Koshits speaks of the progressive role that electronic theories have played and continue to play in organic chemistry. Noting the significance of quantum chemistry, the speaker condemns the position of A. D. Petrov, who calls for rejecting all theories and engaging only in experiment. He believes that, contrary to the opinion of Chelintsev and Batur, there is no crisis of theoretical thought in Soviet organic chemistry. The speaker considers it a shortcoming of the report that it pays little attention to the question of the influence of the external medium on the mechanism of chemical transformations. The speaker does not agree with the report’s recommendation to strive to use a single formula for the depiction of molecules. He points out that in organic chemistry there are many vague, indefinite terms (tautomerism, desmotropy, pseudomerism, mesomerism, etc.).

Corresponding Member of the Academy of Sciences of the USSR S. S. Medvedev said that one of the principal questions that must be resolved at the present conference is the question of the further development of quantum chemistry. At the Physicochemical Institute named after L. Ya. Karpov, “quantum chemistry” alone developed for several years; in recent years all other quantum-chemical directions were displaced by work on resonance theory carried out by Ya. K. Syrkin and M. E. Dyatkina. Thus, theoretical research was artificially narrowed precisely in the most fruitless and methodologically flawed direction. One cannot agree with the pessimistic assessment by Ya. K. Syrkin of the prospects for the further development of quantum chemistry. Ya. K. Syrkin made it appear that before the criticism of resonance theory the methods of quantum mechanics could be applied to the calculation of complex, sometimes even nonexistent molecules, but after its collapse they cannot, although the questions of chemistry have not thereby become more complex. Thus, Ya. K. Syrkin turns out to have lost either resonance theory or nothing. “I think,” said S. S. Medvedev, “that none of those present took seriously this statement by Ya. K. Syrkin.” The speaker then stops...

is reduced to the question of the place of computational quantum-chemical methods in chemistry and notes that they, of course, must play a subordinate role. It is necessary to improve computational methods by drawing more widely on physicists for this purpose. The speaker notes that the report poorly shows the role of structural theory for practice and devotes little attention to the central problem—the question of reactivity*).

The high activity of the participants in the conference clearly demonstrated the timeliness and necessity of holding it, as well as the urgency of the questions raised at it. More than forty people took part in the discussion of the report, and not all who registered for participation in the debates had an opportunity to speak, since the time allotted for the conference was exhausted.

In the resolution adopted by the Conference, it is noted that the successes of the Soviet organic chemical industry are connected with the creative development of organic chemistry in our country. However, alongside fruitful directions in the theory of chemical structure, in recent years there has become widespread the so-called “theory of resonance (Pauling) or mesomerism (Ingold),” developed by Anglo-American scientists. This theory, which preaches the multistructural nature of the molecule, has proved to be opposed to the fundamental propositions of Butlerov’s theory.

“Methodologically vicious, physically untenable and fruitless, the concept of resonance or mesomerism,” the resolution says, “has, unfortunately, found among Soviet scientists its adherents and continuators (Corresponding Member of the USSR Academy of Sciences Ya. K. Syrkin, M. E. Dyatkina, M. V. Vol’kenshtein, A. I. Kiprianov, and others). These scientists, propagating the idealistic and mechanistic concept of resonance, tried to cover the viciousness of this concept by references to the fact that it supposedly follows from quantum mechanics and is therefore called upon to explain all the facts and laws of chemistry. The ‘theory of resonance or mesomerism’ was also uncritically accepted by some other Soviet scientists mentioned in the report. The spread of this ‘theory’ has harmed Soviet chemistry. It diverted the efforts of chemists in the direction of fruitless speculative constructions, creating the harmful illusion of explaining many facts and regularities which in reality remained unexplained.”

“The Conference notes that Ya. K. Syrkin, M. E. Dyatkina, M. V. Vol’kenshtein and A. I. Kiprianov, and others, now recognize the viciousness and fruitlessness of this ‘theory.’ At the same time, the Conference states that in their speeches in the present discussion Ya. K. Syrkin, M. E. Dyatkina, M. V. Vol’kenshtein and A. I. Kiprianov did not give an extensive criticism of the ‘theory of resonance or mesomerism’ and a detailed analysis of their serious methodological and ideological errors.

“...The resolutions of the Central Committee of the VKP(b) on ideological questions mobilized the attention of the Soviet chemical community to questions of the methodology of science and helped to uncover the errors that existed in chemistry and to outline further paths for the development of chemical science on the basis of the only correct dialectical-materialist worldview.”

“The Conference resolves to approve the basic propositions of the report presented by the Commission of the Division of Chemical Sciences of the USSR Academy of Sciences, in which an analysis is given of the present state of the theory of chemical structure, the idealistic essence of the ‘theory’ of resonance or mesomerism is shown, the errors of certain Soviet scientists are exposed, and paths for the further development of Butlerov’s doctrine are outlined.”

*) In the present review, because of lack of space, not all speakers’ speeches are given. (Ed.)

“The conference also considers it necessary to note a number of major shortcomings in the Commission’s report. Thus, the report did not show that ideological distortions in questions of chemical theory are closely connected with hostile theories in biology and physiology and constitute a united front of struggle by reactionary-bourgeois ideology against materialism. It did not characterize the achievements of Soviet organic chemistry; insufficient attention was paid to the kinetics of chemical processes, to the influence of the medium and the nature of chemical reagents...” Having noted a number of other shortcomings in the report and the paramount importance of the creative development of Butlerov’s doctrine, the resolution indicates that, in order to solve the problems of theoretical chemical structure, it is necessary to make broader use, alongside chemical approaches and methods of research that have brilliantly justified themselves, of all the achievements of related disciplines and, first of all, of modern physics with all the wealth of its experimental and theoretical methods.

“In connection with this,” the resolution says, “the conference notes the abnormality of the self-removal of the majority of physicists from participation in the struggle for the creation of an advanced theory of chemical science. It is also abnormal that almost none of the leading theoretical physicists took part in the work of the present conference.”

“The conference states that physical methods of research have not yet received proper dissemination in organic chemistry and considers it necessary to make broad use of spectroscopic, electronographic, mass-spectroscopic, and other methods for the study of the structure and properties of organic compounds... The conference calls upon physicists and physical chemists to take an active part in developing these methods.”

“The conference also notes the insufficient participation of theoretical physicists in the development of quantum chemistry. It is necessary that Soviet theoretical physicists and mathematicians take the most active part in developing the problems of theoretical chemistry and computational quantum-mechanical methods. Only through the joint work of chemists and physicists will the theory of chemical structure become the quantitative theory whose creation A. M. Butlerov called for.”

The conference, in its resolution, further calls upon Soviet chemists to develop theoretical chemistry in every possible way and to introduce the results of scientific work broadly into the national economy. It expresses confidence that, under the leadership of the Party of Lenin—Stalin, Soviet chemists will honorably fulfill the instructions of the great leader of the working people, the brilliant scholar Joseph Vissarionovich Stalin.

In closing the Conference, the chairman, Academician M. M. Dubinin, noted that the followers of the “theory” of resonance had appeared at the Conference acknowledging their mistakes and had briefly analyzed the sources of their errors. “We have no grounds,” said M. M. Dubinin, “not to believe in their sincerity in acknowledging their mistakes. But words must be supported by deeds, and we shall expect from them the promised creative contribution to the development of the genuine Soviet theory of structure. We are obliged to render them the necessary assistance and to create the conditions for work. There is no doubt that, united by the efforts of Soviet chemists, they will honorably fulfill the task of creating an advanced materialist theory of structure in organic chemistry.”

With great enthusiasm the Conference sent a letter of greeting to Comrade I. V. Stalin.

N. D. Sokolov