A
SYMPOSIUM
Three-Dimensional Chemistry
Presumably there never mill he agreement among tdachers as to vhat makes Modern Chemistry courses modern. It seems clear, however, that the knowledge of structures vhich has grown explosively in the past fifty years has, in some quarters a t least, had a major impact on ~ndergraduat~e inst~uction. Attention increasingly has turned toward :attempts to relate known structures to physical properties and chemical reactivity and to account for mechanisms and rates of reactions on the basis of known or assumed structures. It is commonplace, for example, t o relate the properties of water to the structural properties of the water molecule in the gas phase, and t o the additional structural properties arising from interactions among these molecules and their aggregates in the condensed phases. It is surprising (or so it seems to this general chemistry teacher) that most undergraduates beginning their chemistry a t the collegiate level seem to have little or no comprehension of the water molecule (for example) as a threedimensional entity; nor do they even think of it as a two-dimensional or planar entity pictured on a flat sheet of paper. To them it is a formula, HzO. Worse yet, they have not even thought about thinking about it in three dimensions. Without getting involved in discussions of the new mathematics, one might lament in passiug the seeming disappearance of solid geometry from the secondary school curriculum. The adjectives tetrahedral, octahedral, and pyramidal somehow have become chemical terms rather than the words of geometry, and as such are both suspect and subject to misspelling! One wonders what the elegant shaded drawings in many of the newer secondary school chemistry texts mean to the students as they flip the pages. It is encouraging, however, to note that more and more teachers are taking advantage of simply constructed and inexpensive three-dimensional models to point out that nature's building blocks do have three dimensiom, that they really do occupy space, and that it is possible better to understand and better to correlate properties of substances from a knowledge of the structures illustrated by these models. It is not trivial to be conscious of the fact that the methane molecule and the ammonium ion are both isoelectronic and isostructural; that the carbonate ion and the nitrate ion also are isoelectronic and isostructural and are planar; that the sulfite ion and sulfur trioxide are quite different geometrically; that the carbon dioxide molecule, the aside ion, and the
dinitrogen oxide molecule are linear; that cis and trans isomers really are significantly different. These structures just cited may mot be as spectacular as the structures of proteins and other high polymers, both man-made and naturally occurring, but they are more easily and quickly comprehended and can be a good starting point for instructing and interesting the student. With the thought that teachers are interested in keeping their courses abreast of the times in the area of three-dimensional chemistry, and that they are interested in knowing what other teachers are doing, the Division of Chemical Education presented a one day symposium on Three-Dimensional Chemistry a t the LOBAngeles Meeting of the American Chemical Society in April, 1963. Six speakers presented papers, each scheduled for forty-five minutes with fifteen minutes allotted for questions and discussion. The three morning papers, in the area of General and Inorganic Chemistry, were presented by Professors Gillespie, Busch, and Rundle, who treated successively t.he sterenchemistry of small molecular and ionic units, metal complexes, and the crystal chemistry of aggregates of these smaller units or of macromolecules. The three afternoon papers, in the area of Organic Chemistry and Biochemistry, were presented by Professors Eliel, Allinger, and Ingraham. This session began with a general treatment of organic stereochemistry, proceeded to conformational analysis, and finally a discussion of stereospecificity in biochemical reactions. Professor Gillespie's paper, a presentation of VSEPR theory which led off the Symposium, was essentially that which appeared in THrs JOURNAL, 40, 295 (1963). It was planned to publish the five remaining papers in this issue of the Journal, hut the untimely death, in the early Fall of 1963, of Professor Robert E. Rundle of the Iowa State University before his manuscript was completed has reduced this number to four. Those present a t the Symposium will recall Dr. Rundle's lively and animated presentation of crystal symmetry and lattice theory, horidinginillterstitial conlpounds, and especially his colorful visual presentation of some aspects of Cu(I1) halide structures. It is hoped that all of these presentations will bring to teachers ideas that will help them in presenting to their students the chemist's three-dimensional view of his submicroscopic world. John F. Baxter, Symposium Chairman University
of
Florida, Gainesvilie
Volume 41, Number 2, February 1964
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65
