linear ccombinrttion of stomic orbitals (LCAO>molecular orbital thwry and energy calculations. The Hiickel theory is then applied to a number of organic moleculsr and ionic system3. The H t h chapter defines and illustrates the calcul* tions of electron and charge densities, bond order and free valence. The last two chapters extend the Huckel theory to heterocyclic molecules (taking pyrrole as an example) and consider the concept of 2 rule, and aromaticity, Hiickel's 4n the valence bond treatment of benzene. Each chapter is followed by a number of well-chosen problems. A number of chapters include references to the literature. A list of b o o k recommended for additional reading is appended. Although it treats only the simple Hiickel MO theory, the book serves as a useful introduction to the techniques and jargon of the trade. The author states in the preface that juniors and seniors had no difficulty assimilating the material. I n the reviewer's experience the detailed calculations presented for a number of systems, e.g., the ally1 carbanion, illustrate the computational techniques so well that students have little trouble working through the problems a t the end of each chapter or extra problem which are assigned by the instructor. The book stimulates the reader to study the more advanced treatments of the MO thwry of organic systems such as the text by Streitwieser. The book is highly recommended as an introduction to the topic and as supplementary material for courses in valence theory and advanced organic chemistry.
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JOHN R. WASSON Illimis Institute of Technology Chicago
An lntrodurtion to Electron Parmmagnetic Resonance Malcolm Bwsohn, University of Toronto, and James C. Baird, Brown University, Providence, Rhode Island. W. A. Bmjamin, Inc., New York, 1966. Frontiers in Chemistry Series. 274 pp. Figs. and tables. 16 xi X 23.5 em. 513.75.
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The stated purpme of this book is to present an introduction to the fundamentals of electron paramagnetic resonance (EPR) for chemists and biochemists. As such, it is the first book we have with this orientation, and for this reason it could be considered a welcome volume. However, there are a number of faults one can find with it. The book is elementary enough that students and researchers without any quantum mechanical background can read it largely because of its qualitative treatment of the subject matter. But the significant lack of quantitative development results in a, superficial treatment of much of the material. One glaring example is the fact that two chapters are devoted to relaxation phenomena and line shapes and to intensity of spectra, yet the classic Bloch Equa-
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Journal of Chemical Edvcofion
tions, from which so mueh useful information on magnetic resonance Speb troscopy may be obtained, are not even mentioned, nor is there any reference to them in the whole bwk! Largely as a result of their absence, these two chapters lack an adequate base of fundamental principles which would serve to clarify the discussion of the aforementioned topics, and (as is true of mueh of the book) tend to be made up of rather loosely coupled sections. I t also becomes difficult to determine the applicability of certain ideas and definitions to different cases, such as the significance of T? in liquids versus solids, and its relationship to whether the resonance is homogeneously broadened or not. The definition of T2as a spin-spin relaxation time as well as essentially an inverse linewidth is certainly insufficient. In fact it may be said that the treatment of relaxation phenomena for free radicals in the liquids (probably the case of most interest to chemists), is quite inadequate and in many ways contrary to much of what is presently known on the subject. Unfortunately, the reader will not find adequate references on this topic nor on numerous other topics treated in this book. One also gets the impression that this book was put together without sufficient care. For example on p. 3 the reader may be surprised to learn that.: "the g-factor is a dimensionless constant which is a physical property of the electron.. The g-factor is a proportionality constant between the magnetic moment and the angular momentum." Can magnetic moments and angular momentum actually have the same dimensions? On p. 257 one learns that the two apparently different radicals the tetramethyl-1,4dinitrobenzene anion and the 1,4dinitro-2,3,5,6 tetramethyl benzene anion have different splittings. Indeed they do, but only when they are prepared in different solvents! Despite the de-emphasis of a quantitative treatment the authors nevertheless included a short chapter summarizing quantum mechanics. I t is difficult to see how any "beginner" in ESR, who would be interested to learn that "for an electron, there are only two possible values for [the orientation], i.e., approximately 35'15' and 144-45',. . . " (p. 5) could possibly profit from such a br~efsummary of quantum meohanicd formalism or of the incomplete, but quantitative, appendices. The book is perhaps s t its best treating such topics as the appearance of the hyperfine structure in various liquid state free radical spectra. There are also some useful tables on hyperfine splittings and g-values. However, very little is said about the electronic or valence mechan i s m that give rise to hyperfine splittings, and g-shifts. The later chapters on the triplet state, inorganic applications, double resonance, applications of EPR to chemistry and to biology all suffer from the defects already noted. Nevertheless, they do includes. number of interesting topics. On the whole, the book does indicate the great variety of ideas, techniques, and applications currently associated with E P R even though the treatment given is often too sketchy to obtain a usefulunderstanding. This book could probablv have
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been improved had i t been written with more care and planning and with s. greater respect for the knowledge of the reader. Cornell University I t h a , New York
Valence Theory
J. N. Murrell, University of Sussex, England, S. F. A. Kettle, University of Sheffield, England, and J . M. Tedda, University of St. Andrews, Scotland. John Wiley and Sons, Inc., New York, 1965. xiii + 401 pp. Figs. and tables. 16 X 23.5 cm. $7.75. In the preface, the authors state their intention of writing a book "to bridge the gap between the semiqualitative picture given in Coulson's "Valence" and the formal mathematicd account given in Eyring, Walter, and Kimbdl's "Quantum Chemistry!' The aut,hors have achieved their goal. The first five chapters (pp. 1 4 0 ) are introductory. The chapters include (1) The Foundations of Atomic Theory, which leads up to and introduces the Schrodinger equation, (2) The Electron in a Constant Potential, which in a very cursory manner illustrates the quantization of energy, quantum numbers, and zero-point energy, (3) The Hydrogen Atom, which develop the concept of atomic orbitals from sohtiom of the Schrodinger equation,, Many-electron Atoms and the Penod~o Table, which desoribes the n, 1, m, and s quantum numbers and their use for understanding the periodicity of elements, and (5) Basic Principles of the Theory of Valence, which is essentially a qualitative discussion of covalent bonding in terms of molecular-orhital and valence bond theory. The level of material presented in these five chapters is erratic. For example, bonding in simple hydrocarbons is discussed a t a level found in the average general chemistry book, whereas the mathematical justificetion of atomic orbitals is discussed a t an advanced level. In C h a p t,er 5, the concept of symmetry is used to develop the idea of hybridization, even though symmetry is not discussed until Chapter 8. In the next four chapters (pp. 61-1311, the more formal mathematical aspects of quantum theory are described. This materiel includes normalization! Hamiltonian Operstors, eigenvalues, e~genfunctions, Hermetians, variation and perturbation theory, antisymmetry rule, BornOppenbeimer approximations, symmetry groups, group theory, angular momentum operators, Russell-Saunders coupling, flnd parity. I n this part of the book, a n l n e page rigorous treatment of the helium atom is resented to illustrate the techniques for obtaining approximate solutions of the Schriidinger equation. The discussion of symmetry groups could have been greatly aided by more illustrations and lmproved art work. However, the discussion of Hermetian operators is very good. I n Chaptels 10, 11 and 12 (pp. 132-2011
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(Continued on page Al58)
