KURT C. SCHREIBER Duquesne University, Pittsburgh, Pennsylvania
T H E subject of stereochemistry is treated in standard undergraduate organic chemistry hooks in a single chapter usually located in the central portion of such texts.' Outside that chapter, reference to stereoisomerism is generally limited to the discussion of carbohydrates and a brief word under Amino Acids. A twofold criticism can he made against this timehonored presentation of stereochemistry. First of all, in this arrangement the student is not introduced to this aspect of organic chemistry until the closing lectures of the first semester, and, secondly, the topic is presented in a manner isolated from the remainder of organic chemistry. This means that in a course which presents aliphatic chemistry in the first semester and aromatic chemistry in the second, stereoisomerism is discussed a t the tail-end of the study of aliphatic chemistry and usually not considered further in the second semester. This leaves the impression with the student that this type of isomerism is an odd fact to he mentioned, but with which one does not have to he concerned in organic chemistry in general. In recent years an increasing amount of theoretical organic chemistry (organic reaction mechanisms, etc.) has been introduced into elementary organic chemistry cour~es.~This shift makes it increasingly desirable to abandon the above-mentioned practice with respect to teaching stereochemistry. In the undergraduate organic chemistry course given at Duquesne University the subject of stereochemistry is introduced in the following manner. I n the discussion of the reactions of alkyl halides, one of the first classes of compounds studied, the displacement of the halogen atom by nucleophilic reagents is mentioned and illustrated by various examples such as hydroxide, acetate, and iodide ions. Also introduced a t this point is the concept of reaction mechanism, which in this particular example consists of attack by the nucleophilic reagent on the carbon a t which reaction
is oecnrring from the hack side of the bond which is being broken, with inversion of the three groups attached to the center of r e a ~ t i o n . ~This is illustrated with methyl iodide: \
H
