G. Eyring, J. Walter, J. Kimball, Quantum Chemistry, translated by L. I. Kazarnovskaya, edited by M. I. Genkina. State Publishing House of Foreign Literature, 1948.

J. Wheland, The Theory of Resonance and Its Application in Organic Chemistry, translated by M. E. Dyatkina, edited by Ya. K. Syrkin, State Publishing House of Foreign Literature, 1948.

More than twenty years have passed since the first quantum-mechanical interpretation of the nature of the chemical bond was given. During these years many works have been devoted to quantum chemistry; beginning with the study of the simplest hydrogen molecule, scientists at the present time are calculating the values of energy terms in the most complex polyatomic molecules and are applying quantum-chemical methods to the solution of the most diverse problems. Quantum chemistry has taken a prominent place in science, and the material encompassed by it is so extensive that it is now possible to draw certain conclusions. After a period of ardent enthusiasm for the new methods, which, as it seemed, could provide an exhaustive physical explanation of the chemical properties of matter, there came a period of critical examination of the foundations of quantum chemistry, a time of searching for new paths in the theory of molecules, since the limitations of the methods of quantum chemistry are now already evident. At the same time the importance of the theory of the structure and properties of molecules is increasing with each day. Therefore the appearance of two new translated monographs on quantum chemistry should be regarded as a positive fact; together with the books by Soviet scientists devoted to the same field (Ya. Syrkin and M. Dyatkina, Chemical Bond and Molecular Structure; V. Kondrat’ev, Structure of Atoms and Molecules, etc.), they fill a substantial gap in the scientific literature.

The book by Eyring, Walter, and Kimball was written by theoretical physicists and presents a mathematical exposition not only of quantum chemistry, i.e. the quantum mechanics of the molecule, but also of those sections of general classical and quantum physics with which one must become acquainted in order to understand the principles of quantum chemistry. Only the second half of the book (eight chapters out of eighteen) is devoted to quantum chemistry proper. This structure of the monograph (old quantum mechanics, principles of classical mechanics, foundations of quantum mechanics and its mathematical methods, structure of the atom, and only then quantum chemistry) determined the extraordinary conciseness and, one might say, outline-like character of the exposition. At the same time the authors understand by the words “quantum chemistry” not only the theory of the chemical bond in simple and complex molecules, but also the theory of any physical properties of molecules—molecular spectroscopy, statistical mechanics, the quantum-mechanical theory of the rates of reactions, the theory of electrical, magnetic, and optical phenomena (the theory of optical activity), etc. All these questions are set forth in the book, and only two chapters—one tenth of the book—remain for the theory of the chemical bond itself. From the point of view of theoretical physics, the specific weight of the theory of the chemical bond in the general system of quantum mechanics is indeed not so very great, and all questions pertaining to it, having

... of fundamental physical significance are in fact presented by the authors in the two chapters indicated.*)

The specificity of the arrangement of the material has to a considerable extent determined the merits and shortcomings of the reviewed book. This book will not satisfy a chemist-reader interested in quantum theory as applied to concrete substances and processes. Moreover, the book is too difficult for a chemist; the authors evidently had in mind that its reader would be a theoretical physicist with a solid mathematical background. But such a reader, essentially, does not need a summary exposition of the principles of classical mechanics, nor of the elementary problems of quantum theory.

On the other hand, for a physicist studying the structure of molecules, a detailed exposition precisely of the theory of molecules would have been very valuable. In this sense the book by Eyring, Walter, and Kimball disappoints expectations.

The chief merit of the book is its high scientific level and the fact that the main problems of the chemical physics of the present day have found their reflection in it. Especially interesting here is Chapter XVI, devoted to the quantum-mechanical theory of reaction rates. The authors give a detailed theory of the activated-complex (transition-state) method, which belongs to Eyring himself. Valuable is the exposition of the quantum theory of optical activity, in whose development Eyring likewise took a visible part. The brief but sufficiently clear exposition of group theory (Ch. X and Appendix VII) will also be very useful to the reader. At the same time, the chapters in which the general foundations of quantum mechanics are set forth (Chs. I—IX) contain nothing new, and too little space is allotted to questions of molecular spectroscopy and statistical mechanics. On these important questions the reader of the book will obtain only a preliminary and superficial idea.

Just the two small chapters concerning the chemical bond (Ch. XII—Covalent Bond, and Ch. XIII—Resonance and the Structure of Complex Molecules) contain interesting indications and assessments that are usually absent from the literature. Particularly important, and certainly correct, is the indication that the term “exchange energy” has a more mathematical than physical meaning (p. 288), made in connection with the exposition of the work of James and Coolidge. The assessment of the theory of directed valences is significant (p. 296): “this treatment must be regarded as a quantum-mechanical description of the formation of a covalent bond, based to a considerable degree on the preliminary knowledge of experimental facts.” However, the authors do not trouble themselves with an investigation of the fundamental foundations of quantum chemistry and do not characterize the accuracy and reliability of the methods they expound. Therefore the reader is left with the false impression of the equivalence of the basic propositions of quantum mechanics and its application to the theory of complex molecules, which not accidentally has aroused so much controversy in recent times.

On the whole, Quantum Chemistry by Eyring, Walter, and Kimball is a concise survey of the theory of a number of current problems. This survey is composed at a high scientific level, but without the necessary criticism and is not distinguished by depth of thought. The book will be useful to the reader at least because of the absence of a more detailed monograph.

The book by J. Wheland, The Theory of Resonance, has a completely different character. It is a book written for organic chemists, a non-mathematical book and in this sense even more accessible to the reader than the well-known monograph by J. K. Syrkin and M. G. Dyatkina.

The author expounds the theory of electronic resonance without its justification, in the form of certain formal rules (paragraph 1.4—Conditions of Resonance), considering that such a justification can be given only in mathematical form, inaccessible—

) Cf. L. Landau and E. Lifshitz, Quantum Mechanics*, Part I, Gostekhizdat, 1948.

BIBLIOGRAPHY

to the ordinary reader-chemist. Ueland asserts that “these rules, like the very existence of resonance, are only consequences of the fundamental equations of quantum mechanics” (p. 19). To what extent are these consequences obligatory? The author gives an answer to this question on p. 49, in a paragraph which, in view of its importance, we quote in full:

“From the foregoing it is clear that the idea of resonance is a speculative conception with greater scope than other physical theories. It does not reflect any internal property of the molecule itself, but is a mathematical device invented by the physicist or chemist for his own convenience. Indeed, if quantum-mechanical problems could be solved exactly, or if other approximate methods were used, the idea of resonance would not arise. Moreover, if in the Schrödinger equation another set of $\varphi$ (structural functions, M. V.) is used, then the molecule whose wave function approximates the function $\psi$ will be described differently, as resonating among an entirely different series of structures. However, in the following chapters we shall see that these circumstances in no way diminish the practical usefulness of this conception, but they make us always keep in mind that resonance has meaning only in connection with a particular method of approximation to the true state, and that one must constantly take care not to ascribe to the various resonance structures a physical meaning which they do not possess.”

We see that Ueland tries to get to the essence of the theory of resonance and notes the well-known difficulty in its methodological foundations. However, the above quotations testify to the complete confusion of concepts and disorient the reader. Either resonance is a necessary consequence of quantum theory, and then this conception cannot be considered merely a “convenient device,” or it is only a “convenient device,” and then, in applying the theory of resonance, we must take a Machist point of view. In reality resonance is neither one thing nor the other—as it is presented: the theory of resonance has the meaning of a transitional chemical working hypothesis, to a certain extent applying the data of quantum theory. The size of this review does not allow us to dwell on this question in greater detail.

Ueland, with great inventiveness and wit, considers the analogy of electronic resonance with the mechanical resonance of two pendulums. These entertaining pages of the book (pp. 34—45) are devoted to proving the existence of such an analogy and, consequently, to substantiating the term “resonance” as applied to chemical problems. Yet this analogy is formal and unconvincing in character, and, from our point of view, the term “resonance” confuses rather than explains the essence of the matter.

The further exposition is devoted to specific chemical and physical problems (the nature of valence, resonance energy, resonance and static effects, dipole moments, molecular spectra, chemical equilibrium, and chemical reactions). The book presents rich and varied material, valuable tabular data (a table of interatomic distances in organic molecules, pp. 410—424). Unfortunately, the author immediately forgets the precautions he himself expressed in the above quotation. Therefore the numerous qualitative conclusions made concerning concrete chemical questions do not always sound sufficiently convincing, while the physical discussions of molecular spectra and dipole moments are superficial. In the foreword by the editors, G. Ueland is attested as a chemist and at the same time a physicist-theorist. If the former is correct, then the latter sounds implausible: Ueland’s book, devoted to the structure and properties of molecules as a physical problem, is devoid of genuine physical content. This is especially vivid in the chapter on molecular spectra (Ch. VI, pp. 207—236), in which the very complex and unresolved problem of the structure of the electronic spectra of polyatomic molecules is presented as accessible to solution by means of qualitative pseudovisual methods

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the resonance theory. The author, to be sure, stipulates that the agreement of the calculations of Sklar and Förster with the observed bond lengths is doubtful (p. 232), but he does not explain the reasons for this and does not give a considered assessment of the application of the resonance theory in spectroscopy.

Thus, Wheland’s book can be of value only as a compilation of material and as a qualitative exposition of the resonance theory. The analysis of the fundamental principles of the theory given in the book is confused and methodologically flawed. Meanwhile, the need for such an analysis is very great. This is also indicated by the editors of the book, who note that “at the present time the resonance theory is being subjected to scientific criticism by Soviet scholars from various points of view.” Obviously, the appearance of Wheland’s book in Russian is justified by the fact that it provides some material for such criticism. The urgent task of Soviet physicists, chemists, and philosophers of natural science is to establish a unified materialist point of view on contemporary theories of molecular structure, and to criticize the methodologically and, consequently, scientifically erroneous views of a number of foreign scientists, including Wheland. Such a path will most likely lead to the goal—the construction of a genuinely scientific theory in chemistry.

The Soviet reader will look forward impatiently to the appearance of Soviet monographs devoted to questions of molecular structure, quantum chemistry, and the theory of electronic resonance, satisfying the high requirements that we must set for their scientific and methodological content. We see that the books under review do not satisfy these requirements.

It is characteristic that the authors of both books completely ignore Soviet scientific works in the field of quantum chemistry and molecular structure. Yet these works are significant both quantitatively and qualitatively. Let us point to the numerous works of Prof. Ya. K. Syrkin and his school on the resonance theory, the works of the Leningrad physicists on molecular spectroscopy, the works of the schools of Academician S. I. Vavilov, Academician A. N. Terenin, Academician A. E. Porai-Koshits, and many others. The authors’ ignorance of these works in the books under review does not speak in their favor.

The translations of both books have been very well done. The appearance of the books is excellent. It would be desirable that not only translated but also Soviet books be published at the high level characteristic of all the publications of IL.

M. Volkenstein