BOOKS
A Balanced View of Symmetry Reviewed by Bart Kahr everal years ago, Edgar Heilbronner, professor emeritus at the University of Basel in Switzerland, wrote an article called "Why Do Some Molecules Have Symmetry Dif ferent from that Expected?" in which he considered the contor tions molecules will sometimes suffer in order to look less perfect than a chemist's intuition would expect. Jack D. Dunitz, professor emeritus at the Swiss Federal In stitute of Technology (ΕΤΗ) in Zurich, has been challenged by entropy's incursion into the otherwise mathematical crystal lattice. His work em phasizes molecules in crystals that choose to be unrelated by symmetry. These men have collaborated to offer '"Reflections on Symmetry in Chemistry .... and Else where/' a view of symmetry by two sci entists who are suspicious of it. They betray their suspicion in describ ing the book's first figure, a landscape painting by the early 20th-century Swiss artist Ferdinand Hodler. "Fortuitous symmetrization, such as reflection in a calm mountain lake, can surprise and please us," Heilbronner and Dunitz write. "[0]n the other hand, its pictorial representation can all too easily acquire an element of kitsch." Hodler was able to walk the fine line between symmetry and asymmetry in his painting, they ex plain. Although he divides the picture horizontally between image and reflec tion, blue hills on either side of the lake rise to unequal heights, clouds are not formed in the same way in all quadrants of the picture, and the details of colora tion also thwart the double-mirror sym metry that the painting appears to have at first glance. That fine line between symmetry and asymmetry is what draws many scien tists to study symmetrical systems in na ture. We need symmetry as a simplify ing and organizing principle. But what is really satisfying—both imaginatively and emotionally—is a small asymmetry. "Reflections on Symmetry" had its or igins in a lecture Heilbronner delivered
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with the stitching on a baseball, but only an initiate knows it. Heilbronner and Dunitz do not rely on symbols or jargon. Instead, symmetry principles are beautifully rendered in the accompanying graphics by Ruth Pfalzberger. The overall design of the book is striking. Cartoons, text, historical documents, chem ical structures, and photographs of models are combined in a natural way. No one element is dominant, even though the goofy, childlike illustrations Hodier strongly attract attention. Who "Thunersee" by Ferdinand would have thought, before see ing Pfalzberger's drawing, that the ethanol molecule and a poodle are isoSymmetry or the lack of it, morphous? In his study of children's drawing, in chemistry as in art, Howard Gardner, professor of education at Harvard University, observes that "in does more than describe striving for symmetry, the child instead nature, it can also appeal achieves balance." The work of very young artists is apt to be a bit lopsided; to the inner spirit they lack the skills to achieve symmet rical precision. Even so, the result can "Reflections on Symmetry in Chemis often be a balanced or well-composed try and Elsewhere," by Edgar Heil picture. Accomplished artists like Hod bronner and Jack D. Dunitz, VCH Pub ler or Pfalzberger, on the other hand, lishers, 220 East 23rd St., New York, N.Y. can achieve symmetry but strive for balance. 10010,1993,154 pages, $39.50 Scientists expect symmetry and de light when nature instead provides bal in 1980 as part of a series examining the ance. For example, Kenneth B. Wiberg interface between art and science. There and colleagues at Yale University recent he tried to convey how systematic think ly prepared the highly strained hydro 1,3 ing about symmetry, or the lack thereof, carbon, tricyclo[2.1.0.0 ] pentane. has guided chemistry from its infancy Quantum mechanical calculations show in the early 19th century through de that the expected twofold symmetry is velopment of the principles of orbital absent in the ground state. The opti symmetry and the discovery of quasi- mized structure is appealing in a way crystals. In the book, he and Dunitz in that the ideal structure would not be. troduce concepts of symmetry pictorial- The absence of symmetry is the best ly as they describe seminal contributions part; it reveals a great molecule behind a to the understanding of how matter is difficult synthesis. organized. They do it in 150 pages, play Wiberg doesn't fuss about this ab fully, but without compromise. sence of symmetry nearly so much as I How? Some chemists associate symme do. After all, modern organic chemists try with an arcane symbology that makes no longer delight in the energetic tri applications of group theory to chemistry umph of the chair form of cyclohexane seem complex and forbidding. Such sym over the planar one. They have explana bols as D2d, B2, and P42m all refer to ob tions for this sort of thing. But I am sure jects that have something in common that Hermann Sachse's (1862-93) con1 $ .£ | | g | |
temporaries smiled when he first fashioned the twisted and bent conformations of cyclohexane. Although there are many excellent books about symmetry in art and science, "Reflections on Symmetry" is unique in its treatment of the historical development of structural chemistry and crystallography. In one chapter of less than 30 pages, the authors move from the early efforts of 19th-century Swedish chemist Jons Jakob Berzelius to construct chemical models to the recent synthesis of polyhedral fullerenes, with writing so fluid that one is convinced nothing important was left out. The chapter has a symmetry of its own. Its last figure, an illustration of the Coulomb explosion of H3+, gives a picture of a molecule no different from John Dalton's "compound atoms" that began the chapter. In some ways, the chapter implies, the science of chemistry has been a great effort to justify our intuitive notions about symmetry. "Reflections on Symmetry" slows down as it passes into a discussion of the
Cahn-Ingold-Prelog (CIP) system for specifying stereocenter configurations. Not only does it offer the basic rules, but they are applied to tricky molecules such as the trihydroxyglutaric acid stereoisomers. The problems encountered in such applications do not have a geometrical flavor. The abrupt mood change is compounded by an incorrect Fischer projection of one of the meso-fovms. If the world is asymmetric and tilted, or "chiral and clinal" as one of the authors of the CIP system, Vladimir Prelog, described it, why does symmetry seem intuitive? Why are scientists so often seduced into proposing a symmetrical solution to a problem? Take, for example, the weird hexagonal structure for calcium stéarate imagined by the French chemist Marc Antoine Augustus Gaudin (1804-80). Rather than a long-chain structure appropriate for a fatty acid derivative, he proposed something that resembles a snowflake. Similarly, most physicists were astonished by the nonconservation of parity in weak nuclear interactions. And a complex in which
tetracyanoethylene sits squarely athwart one of the two rings of naphthalene seems, somehow, cockeyed. "Reflections on Symmetry" is grounded in such fairly esoteric examples. They make it more interesting than most books on symmetry; they make it well composed, balanced. To restore balance to this essay, we should return to Hodler's landscape. Reading "Reflections on Symmetry," I was certain I had seen this picture before. In his 1974 book "Art and Visual Perception," psychologist Rudolf Arnheim produced a stylized version. He describes it this way: "The basic composition is completely symmetrical around a horizontal axis, and almost symmetrical around the central vertical. By turning nature into ornament, the artist has obtained a chilly preponderance of order." Where Heilbronner and Dunitz see dynamism in the absence of a perfect reflection, Arnheim sees a frozen lake! Is symmetry in the eye of the beholder? Is one person's balance merely symmetry to another? To the organic
NOTICE OF JOB VACANCIES ORGANIZATION FOR THE PROHIBITION OF CHEMICAL WEAPONS THE HAGUE, NETHERLANDS The U.S. Government has been provided with vacancy notices for inspector trainees for the new Organization for the Prohibition of Chemical Weapons (OPCW), upon entry into force of the Chemical Weapons Convention (CWC), which is expected to be January 1995. The Provisional Technical Secretariat of the Preparatory Commission for the OPCW is charged with training inspectors for the OPCW prior to entry into force of the Convention. The OPCW will be an international organization located in The Hague, Netherlands. These 215 positions which require highly qualified individuals in the chemical, chemical engineering and related fields are: P-3/P-4 Level Inspectors: Analytical Chemist CW/Munitions Specialist Chemical Production Logistician Chemical Production Technologist Industrial Chemist Medical Specialist
GS-6/GS-7 Level Inspection Assistants: Technician Para-Medic
FOR INFORMATION AND APPLICATIONS CONTACT: Mary Fannin, (202) 647-8018 Eugene Klimson, (202) 647-8777 FAX: (202) 647-7663, of the U.S. Arms Control and Disarmament Agency, 320-21 st St, NW, Washington, DC. 20451 Application Deadline: March 2 9 , 1 9 9 4 CIRCLE 6 4 ON READER SERVICE CARD MARCH 14,1994 C&EN
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Environmental Chemistry of Lakes and Reservoirs
Presents a timely explo ration of research topics in environmental chemistry of lakes and reservoirs. Includes cover age of: • Methodological advances in studies of lake geochemistry • Cycling and distribution of major elements in aquatic systems • Behavior of trace metals, with an emphasis on processes that control their solubility and transport • Behavior and face of organic contaminants Environmental Chemistry of Lakes and Reservoirs is valuable reading for chemists, environmental engineers, biologists, and scientists involved in practical aspects of water pollution. Lawrence A. Baker, Editor Advances in Chemistry Series No. 237 620 pages (1994) Clothbound ISBN 0-8412-2526-5 — $149.95 Order from: American Chemical Society Distribution Office, Dept. 74 1155 Sixteenth Street, NW Washington, DC 20036 Or CALL TOLL FREE 1-800-227-5558 (in Washington, DC, 202-872-4363) and use your credit card! FAX: 202-872-6067. ACS Publications Catalog now available on internet: gopher acsinfo.acs.org
ACSIIIPUBUCAHONS Essential Resources for the Chemical Sciences
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BOOKS chemist, the structure of benzene in the solid state is a symmetrical hexagon; to a crystallographer, it isn't quite. Even though the six carbon-carbon bonds are measured to be just about the same length in the crystal, space group sym metry tells us they cannot be exactly equal. A new theme is developing in chemis try as several groups of investigators have begun to quantify such formerly qualita tive attributes of molecules as chirality and symmetry. Researchers at Princeton University, for example, want to know if some things are more chiral than others. Most chemists would agree that CFClBrI seems more chiral—more asymmetrical— than CF 1 H 2 H 3 H, where three of the atoms differ from each other only by the number of their neutrons. Before a mathe matical foundation was developed by Kurt Mislow and coworkers at Princeton to compare geometric figures, such "de grees" of chirality seemed heretical. In the past few years, David Avnir and his colleagues at the Hebrew Uni versity in Jerusalem have developed new algorithms for deciding how far a geometric object has been distorted from some symmetry that is considered ideal. In so doing, they have extended the re search of Dunitz, among others, who first gave precise meaning to statements such as "the molecule has approximate Td symmetry." The challenge remains to
make this new rigorous thinking about chirality and symmetry stereochemically productive. Perhaps research on fullerenes in some ways characterizes the chemistry of the 1990s. As soon as chemists got hold of the icosahedral Cœ, the rush was on to break its symmetry. A variety of addends have decorated fullerenes, gobbling up its symmetry along the way. Putting an atom inside a fullerene could preserve the symmetry of the host, unless the atom refuses to take the symmetric position and instead sticks to the host's interior walls. Collectively, chemists seem like children who will build elaborate symmetric structures out of sand or snow, all the while eager to trample them. Artists like Hodler are called Symbolists. The categorization does not mean that he was comfortable with terms like D2d, B2, and P42m. It identifies Hodler as part of a romantic tradition in painting that rebelled against 19th-century realism. Art, he believed, is a product of the inner spirit, not of nature observed. In "Reflections on Symmetry" Heilbronner and Dunitz show us that symmetry, or the lack thereof, can appeal to our inner spirit; it does more than describe nature. Hodler would have liked this book. Bart Kahr is an assistant professor of chemistry at Purdue University where he studies the growth, structure, and physical properties of crystalline solids. Π
Data Analysis for the Chemical Sciences: A Guide to Statistical Techniques. Rich ard C. Graham, xx + 536 pages. VCH Publishers, Distribution Center, 303 Northwest 12th Ave., Deerfield Beach, Ha. 33442-1705.1993. $65.
Hazardous Materials and Hazardous Waste Management: A Technical Guide. Gayle Woodside. xxiii + 383 pages. John Wiley & Sons, 605 Third Ave., New York, N.Y. 10016.1993. $59.95.
Electroanalytical Chemistry: A Series of Advances. Vol. 18. Allen J. Bard, edi tor, xii + 400 pages. Marcel Dekker, 270 Madison Ave., New York, N.Y. 10016. 1993. $165. Environmental TQM. 2nd Ed. John T. Willig, editor, viii + 340 pages. Mc Graw-Hill, 1221 Ave. of the Americas, New York, N.Y. 10020. 1993. $47. Fluorescent Chemosensors for Ion and Molecule Recognition. ACS Sympo sium Series 538. Anthony W. Czarnik, editor, χ + 235 pages. American Chem ical Society, 1155—16th St., N.W., Washington, D.C. 20036. 1993. $69.95. Fluorinated Surfactants: Synthesis, Prop erties, Applications. Erik Kissa. xii + 469 pages. Marcel Dekker, 270 Madison Ave., New York, N.Y. 10016.1993. $165.
Hazardous Waste Site Soil Remediation: Theory and Application of Innovative Technologies. David J. Wilson, Ann N. Clarke, editors, χ + 567 pages. Marcel Dekker, 270 Madison Ave., New York, N.Y. 10016. 1993. $165. Industrial Noise Control: Fundamentals and Applications. 2nd Ed. Lewis H. Bell, Douglas H. Bell, xiv + 660 pages. Marcel Dekker, 270 Madison Ave., New York, N.Y. 10016. 1993. $150. Invention: The Care and Feeding of Ideas. Norbert Wiener, xxiv + 159 pages. The MIT Press, 55 Hayward St., Cambridge, Mass. 02142.1993. $19.95. Legends in Their Own Time: A Century of American Physical Scientists. An thony Serafini. xv + 831 pages. Plenum Press, 233 Spring St., New York, N.Y. 10013. 1993. $27.50. Π
