Early ... Intro Picture

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F. A. Cotton



Cotton was born in 1930 in Philadelphia, USA. He received his Ph.D. from Harvard University in 1955 under Wilkinson. Full Professor at MIT in 1961 (Inorganic Chemistry), since 1972 Professor at Texas A&M University.

To his name there are some 1500 publications and reviews. One can find further an older biography, Sept. 2001, here in archive; a newer one and publication data (both in PDF) here.

Of course everybody knows the Cotton/Wilkinson, Inorganic Chemistry ? And most chemists had to go through F.A. Cotton, Chemical Applications of Group Theory.
(The pictures on the left stem from the above publication.)

After the appearance of Cotton's book Chemical Applications of Group Theory, among some others, it became quite obvious to the students of the mid-sixties that chemistry might profit profoundly from these new and exciting thoughts. It was the beginning of an extremely hopeful area - at least this was what was thought in these days...
The following first three pages of the book might demonstrate that feeling (reduced quality, 50 KB) :

Preface Introd1 Introd2


This book is the outgrowth of a one-semester course which has been taught for several years at the Massachusetts Institute of Technology to seniors and graduate students in chemistry. The treatment of the sub ject matter is unpretentious in that I have not hesitated to be mathemat ically unsophisticated, occasionally unrigorous, or somewhat prolix, where I felt that this really helps to make the subject more meaningful and comprehensible for the average student. By the average student, I mean one who does not aspire to be a theoretician but who wants to have a feel for the strategy used by theoreticians in treating problems in which symmetry properties are important and to have a working knowledge of the more common and well-established techniques. I feel that the great power and beauty of symmetry methods, not to mention the prime importance in all flelds of chemistry of the results they give, make it very worthwhile for all chemists to be acquainted with the basic principles and main applications of group theoretical methods.

Despite the fact that there seems to be a growing desire among chem ists at large to acquire this knowledge, it is still true that only a very few, other than professional theoreticians, have done so. The reason is not hard to discover. There is, so far as I know, no book available which is not likely to strike some terror into the hearts of all but those with an innate love of apparently esoteric theory. It seemed to me that ideas of the sort developed in this book would not soon be assimilated by a wide community of chemists until they were presented in as unpretentious and down-to-earth a manner as possible. That is what I have tried to do liere. I have attempted to make this the kind of book which “one can read in bed without a pencil,“ as my colleague, John Waugh, once aptly described another textbook which has found wide favor because of its down-to-earth character. *

* This statement is actually (and intentionally) not applicable to parts of Chapter 3 where 1 have made no concessions to the reader who refuses to inspect steric models in conjunction with study of the text.

In Sweden they seem to view it entirely diffent :



The experimental chemist in his daily work and thought is concerned with observing and, to as great an extent as possible, understanding and interpreting his observations ün the nature of chemical compounds. Today, chemistry is a vast subject. In order to do thorough and produc- tive experimental work, one must know so much descriptive chemistry and so much about experimental techniques that there is not time to be also a master of chemical theory. Theoretical work of profound and crea- tive nature requires a vast training in mathematics and physics which it is now the business of specialists to deal with. And yet, if one is to do more than merely perform experiments, one must have some theoretical framework for thought. In order to formulate experiments imaginatively and interpret them correctly, an understanding of the ideas provided by theory as to the behavior of molecules and other arrays of atoms is es- sential.

The problem in educating student chemists — and in educating our selves — is to decide what kind of theory and how much of it is desirable. In other words, to what extent can the experimentalist afford to spend time on theoretical studies and at what point should he say, “beyond this I have not the time or inclination to go“? The answer to this ques tion must of course vary with the speeial field of experimental work and with the individual. In some areas fairly advanced theory is indispensa ble. In others relatively little is really useful. For the most part, however, it seems fair to say that molecular quantum mechanics, that is, the theory of chemical bonding and molecular dynamics, is of general importance.

As we shall see in Chapter 5, the number and kinds of energy levels Which an atom or molecule may have are rigorously and precisely deter mined by the symmetry of the molecule or of the environment of the atom. Thus, from symmetry considerations alone, we can always tell what the qualitative features of a problem must be. We shall know, with out any quantitative calculations whatever, how many energy states there are and what interactions and transitions between them may occur. To put it another way, symmetry considerations alone can give us a complete and rigorous answer to the question “What is possible and what is completely impossible?“ Symmetry considerations alone cannot, how- ever, teil us how likely it is that the possibie things will actuaiiy take piace. Symmetry can teil us that, in principle, two states of the system must differ in their energy, but only by computation or measurement can we determine how great the difference will be. Again, symmetry can tell us that only certain absorption bands in the electronic or vibrationai speetrum of a molecule may occur. But to iearn where they will occur and with what intensity, calculations must be made.

Some illustrations of these statements may be helpful. Let us choose one illustration from each of the four major fields of application which are covered in Part II. In Chapter 6 the method of constructing hybrid orbitals will be explained. lt will be shown, inter alia, that a set of sp3d hybrid orbitals will form bonds directed to the apices of a trigonal bi- pyramid if the d orbital used is dx2-y2 whereas the set will form good bonds to atoms at the apices of a square pyramid if the d orbital used is dz2 or dxy The connection between the symmetry of the resulting set of hybrids and the d orbital used is absolutely rigorous on the basis of sym- metry alone, but only by calculations (which are not practicable at present) could we determine which set of hybrids and hence which sym- metry would be favored in a particular molecuie. In Chapter 7 the sym- metry and some other properties of moiecuiar orbitals will be discussed. lt will be shown, for example, that in symmetrical molecules the calcula- tion of the energies of pi molecuiar orbitals can be accompiished by solv- ing severai sets of very smali equations rather than one large equation, but the numerical accuracy of the resuits will still depend on how much labor we wish to put into computations. In Chapter 8, using symmetry arguments and only the most elementary quantitative considerations, we will learn how to construct energy level diagrams, which teil us a great deal about the order of the levels and the qualitative features of the spectra of the ions, for metal ions in ligand fieids. Finally, in Chapter 9 it will be shown that using symmetry considerations aione we may pre- dict the number of vibrational fundamentais, their activities in the infra- red and Raman, and the way in which the various bonds and interbond angles contribute to them for any molecule possessing some symmetry. The actual magnitudes of the frequencies depend on the interatomic forces in the molecule, and these cannot be predicted from symmetry properties.

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Copyright © Nov. 18, 2001 by U. Anders, PhD.
e-mail Udo Anders : udo39@t-online.de

Last updated : May 4, 2003 - 10:22 MEST