Chemical Education Today
Book & Media Reviews
Free Energy Relationships in Organic and Bio-Organic Chemistry by Andrew Williams The Royal Society of Chemistry: Cambridge, UK, 2003. 278 pp. ISBN: 0854046763. Price: $99 Reviewed by Richard Pagni
Free energy relationships, which were independently discovered and developed by Brønsted and Hammett in the early 1920s, have been of inestimable importance in the elucidation of organic and bio-organic reaction mechanisms in the intervening eight decades. Unfortunately, I suspect that most organic chemists have little more than a rudimentary knowledge of this vast and very important subject. Even though I have taught the fundamentals of the subject on numerous occasions to graduate students and upper division chemistry majors and have successfully used the methodology in one of my research papers (1), I feel inadequate on the rare occasions when I read a paper dealing with a bio-organic reaction mechanism. All of us know that there is just too much material for any scientist to master these days. Nonetheless, if the need arose, for example, in a research project, where would a mechanistic, physical, or even a synthetic organic chemist go to become more fluent in the use of free energy relationships? What is a good resource when we teach this material to undergraduate and graduate students? I believe the answer to both questions is the book under review: Free Energ y Relationships in Organic and Bio-Organic Chemistry. Andrew Williams of the University of Kent (England) has written three other books and has studied the mechanisms of organic and bio-organic reactions for close to 40 years. The book, which contains seven chapters, opens up with an introductory discussion of free energy relationships. There is then a very nice write-up on the fundamental equations used in free energy relationships. These include the very familiar Hammett and Brønsted equations from which the myriad sigma constants and α and β values are derived and those, perhaps less familiar, from which acidity functions and solvent nucleophilicities, ionizing powers, and polarities are determined. This is the material of which most organic chemists will have some knowledge. The next chapter on effective charge was new to me. Effective charge is a modern and very powerful tool in understanding reaction mechanisms. The author then devotes a chapter to multi-parameter correlations, which often give better fits of data than
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single parameter correlations. Anyone familiar with kinetics of solvolysis reactions will have heard of the Yukawa-Tsuno equation, for example. One will also find here a discussion of Swain’s and Lupton’s dissection of sigma constants into F (field) and R (resonance) parameters. The following chapter is devoted to coupling of bond-making and bond-breaking in displacement reactions such as SN2 reactions. This is the material where I really saw the power and sophistication of free energy relationships in elucidating reaction mechanisms. The penultimate chapter deals with anomalies, special cases, and non-linearity where topics such as Marcus curvature, reactions with α values greater than one, the so-called ortho effect, and temperature effects are described. The book ends with a discussion of applications where the methods described in the earlier chapters are put to use in determining the mechanisms of several important reactions. The book contains still more. There are, for example, a large number of excellent, thought-provoking problems at the end of each chapter and equally good answers at the end of the book. Each chapter also contains an extensive list of references to the specific material discussed therein and a list of further readings, usually consisting of review articles where the topics of the chapters are presented in great detail. There are, in addition, four appendices. What caught my eye in particular here are the 11 beautiful tables in the third appendix and seven in the fourth. One of the tables lists six sigma constants and F and R parameters for close to 300 substituents, a tour de force. Another lists the rho values for close to 50 reactions. There is little to complain about the production of this sophisticated book, a trait that is common to books published by the Royal Society of Chemistry. It is well written throughout, contains very few typographical and grammatical mistakes, and the drawings and figures are also more than adequate. The book would be a nice supplement to a larger tome used in a senior or graduate level course in organic or physical organic chemistry. It would be an excellent textbook for a specialty course in free energy relationships. Literature Cited 1. Pagni, R. M.; Peebles, W.; Haddon, R. C.; Chichester, S. V. J. Org. Chem. 1990, 55, 5595.
Richard Pagni is in the Department of Chemistry, University of Tennessee, Knoxville, TN 37996-1600;
[email protected] Vol. 81 No. 6 June 2004
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