R+.mt O& tkc New England Association of
Gordon G. Evans Tufts University Medford, Massachusetts
Stereochemistry in the Terminal Course
If chemistry is to he the vehicle of elementary instruction in science, we should begin with stereoisomers and proceed (if we have time) to the simple compounds of oxygen, hydrogen, and nitrogen." This statement appeared in 1920 in a hook by Norman Robert Campbell, a physicist.' There are obvious objections to it, probably not even Campbell expected it to he taken at face value, and certainly no one would do so nowadays. Nevertheless, the statement was made with a serious purpose which merits consideration. It should be explained that the phrase "terminal course," as used in the present article, will refer not so much to a course taken by future biologists and engineers, who may make professional use of chemistry without specializing in it, as to a course taken by students majoring in history, foreign language, philosophy, and so on, who have a science requirement to meet. These students will make no professional use of chemistry; they are commonly required to take a course in science in the hope that they will benefit, as educated individuals and citizens, from some acquaintance with scientific thought. The instructor in a chemistry course intended for such students has hoth a unique opportunity and a unique responsibility. Since he is not required to prepare his students for further work in the subject or to correlate his course with other science courses, he has the opportunity to select with an absolutely free hand the topics which his course shall cover. At the same time, he has a counterbalancing responsibility: he must take care to select those topics which will be of genuine value to the particular group of students with whom he is dealing; he is not justified in including a topic simply because every practicing chemist must be familiar with it. It is fair to say that hoth this opportunity and this responsibility have received less attention than they should have.
'CAMPBELL, N. R.,"Physics: the Elements," Cambridge University Press, London, 1920, Chap. 8; reprinted in S c i m e , 125, 803 (1957). Presented before the Division of Chemical Education at the 144th Meeting of the American Chemical Society, Loa Angelee, California, April, 1963. -438 / Journal of Chemiwl Education
I n making his free selection of course material, the instructor must accordingly have a clear conception of purpose. It is here contended that the primary purpose of a terminal course is--or should he-neither to impart a collection of chemical facts nor to present the current state of chemical theory; it is rather to show, by means of chemical examples, how science operates. The important thing is not what chemists believe, hut the processes by which they arrive a t their beliefs-the search for objective fact, the creation of theory, the interplay of fact and theory, and the perpetual modification and correction and growth which are so characteristic of science. I n other words, the first aim of a terminal college course in chemistry, or in any other science, is to teach science as an intellectual activity, and thus as one of the liberal arts. Such a course will include plenty of important facts and theories, hut they will not be an end in themselves; they will he a means to the comprehension of chemical thought. This is the kind of teaching which will help to ensure that the average citizen of tomorrow shall have a better understanding of science than the average citizen of today. Campbell's argument, in the context of the sentence quoted above, is similar: namely, that the ideas of a science, which originate in the minds of men, are more significant in conveying an appreciation of the subject to the uninitiated than are the impersonal facts of the physical world, however fascinating the facts may appear to persons already scientifically inclined. If all this be granted, it is clearly appropriate in a terminal course to devote much time to the origin and development of a few important chemical concepts; there is no better way to impart insight into scientific patterns of thought. Among these concepts, that of the molecule occupies a conspicuous place; not only is it absolutely indispensable for any introductory study of chemistry, hut also it has evolved through a highly instructive sequence of stages. The original concept of the molecule-the first of these stages of development-viewed it simply as the unit particle of a substance, consisting occasionally of a single atom but usually of several atoms clustered together; this concept dates hack to Lomonosov, Higgins, and Dalton. Many years later, a second stage of development was brought about in the structural theory
of Kekul6, Couper, and Butlerov, which introduced the idea of discrete bonds between the atoms within a molecule. The third stage was reached when van't Hoff and Le Bel proposed the tetrahedral carbon atom and thereby-in mathematical terminoloa-replaced a topological concept of molecular structure by a geometrical one. The introduction of electronic theories of the chemical bond constituted the fourth stage. Now, of these four stages, it is unquestionably the third which has received the least attention in terminal courses in chemistry. I t is the purpose of the present article to suggest that this omission should be reconsidered. One can hardly maintain today that the study of chemistry should start with stereochemistry: when Campbell took this position in 1920, stereoisomerism represented the highest development of the most characteristically chemical concept, while the theory of the structures of simple molecules was in a much less satisfactory state; but this, of course, is no longer true. There remain, however, other reasons why the inclusion of stereochemistry is appropriate at a later point in the terminal course. Five of these may be mentioned here. One noteworthy aspect of the topic is the small amount of scientific background knowledge required for its study; aside from the concepts of atoms and bonds, it is entirely geometrical and is open to direct demonstration. Moreover, the simple principles of stereochemistry lead to a great variety of individual situations; an instructor thus has abundant material from which to select illustrations and problems, and may develop the subject in greater or lesser depth as circumstances require. Third, stereochemistry is still an active field of research, and therefore provides one of the few possibilities for bringing students, even in a terminal course, clear up to the "growing edge" of chemistry through study of topics of current interest to chemists. I
