Stereochemistry Makes the World Go "Round" We live in a three-dimensional world, composed of threedimensional molecules, and yet much of what is taught in the introductorv chemistrv courses implies that chemistrv is a two-dimenshal science. No wonder students find chkmistry Y l a ~ "and unconnected to the "real world". Closer examination reveals just how muchof our livesare affected by the shapes of the molecules runtrolling critiral reactions. The ability of our bodies to fight offa diseaseorganism is partially on their being able to produce an antibiotic . dependent . molecule that will "fit" theprotein on the organism's capsule. The smell of a delicious dinner can only be perceived because the shapes of the odor molecules are compatible with the receptor sites. A similar phenomenonallows several different molecules to taste sweet, but the differences in their structure means that some of them are able to fit the right enzymes and to be metabolized and that others are not-thus providing the no-cal sweetners for the diet-conscious. Everywhere we look we can find examples of stereochemistry making our lives possible-or just more enjoyable. Many of these examples fall into the area usually defined formally as "organic chemistry", but stereochemical concepts are important in other areas, too, and these are all represented in a series of articles in this issue. As our cover so colorfully illustrates, doing the computations to model three-dimensional molecules has been made much easier as more powerful personal computers and the appropriate software has become available. Lipkowitz (page 275) argues that it is now imperative to introduce this kind of computational chemistry into the undergraduate curriculum. He shows how he uses the interesting relationships between the molecular structure of esters and their odors as the unifying concept for the laboratory and computer exercise he has developed. Another way that increased computational power has heen applied to stereochemical questions has been in the calculation of the number of possible isomers of a specific formula. This problem has been around almost since the we first recognized the existence of isomers, but Davies and Freyd (page 278) show how to use modern concepts such as tree theory and a personal computer to calculate not only the number of theoretical isomers but also which of these can actually exist. They put their approach to work to calculate the formula of the smallest alkane that has more realizable isomers than there are particles in the observed universe. While it is impressive that technological advances mean that many of these calculations can now be done by undergraduates, they must first learn the basic concepts of stereochemistry and sometimes these ideas are best presented with concrete, low-tech models. Several articles in this issue give directions for making inexpensive models of important geometric shapes. Vittal (page 282) gives a template and directions for constructing a paper model of buckminsterful-
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Journal of Chemical Education
lerene, a large organic cluster molecule that is currently germane to some interesting research. Yamana (page 301, 302) presents two more of the many models that he has designed from folding a sealed business envelope; these models have many applications in inorganic structure and crystallographic considerations. Knowing the structure of a compound is so important that much of the efforts of analyticel chemists are directed toward this goal and toward developing more powerful techniques to accomplish this. The most popular of the new techniques are those that employ Fourier transforms. Chesick (page 283) presents a comprehensive three-part review of the use of Fourier analysis for structure determination; this issue contains Part 11, which discusses pulse NMR and NMRimaging. Teaching students how to apply the concepts of spectral analysis accurately is not always easy; Reid (page 344) presents an experiment that provides a lessod in what happens if second-order analysis is routinely ignored. Today, we regard the importance of stereochemistry as a given, but examination of the history of the development of these ideas shows how radical they seemed a t the time. Kauffman and Bernal (page 293) explore Werner's early work in determining the structure of coordination compounds, showing how he overlooked the implications of similar work taking place in organic chemistry, retarding his own progress.
The Cover One of the most fascinating aspects of chemistry is the diversity and complexiry of three-dimensional shapes found in organiccompounds. As we discussed above, recent enhancements in the power of microcom~ntershave increased the ease with which we can view graphic representations of molecules. The variety offormatsthat isavailableereatlv facilitates thestudv of intramolecular interactrons as well as the "fit" 01 molecules together in pairs or larger groups. These studies are of critical importance to areas of chemistry as diverse as the mode of action of peptide hormones and the development of ordered matkrks for practical applications. For example, the chiral molecule pict&ed on the cover in bbth ball-and-stick and spacefilling representations is currently being studied by Professors Raymond E. Davis and James K. Whitsell a t the University of Texas a t Austin in order togain an understanding of the influence of molecular handedness and symmetry on crystal packing. Such studies have potential applications in the design of optical switching devices.
