Analyze Your Approach To the Editoc
Molecular Structure and Chlralliy To the Editoc
In an editorial in this Journal [1988, 65, 951 entitled "Communicating: The Students' Obligations," Lagowski described a lecture situation in which some students read newspapers, wrote letters, worked on assignments for other classes, engaged in conversations with other students, or fell asleep. As a teacher of many years I would certainly hope that there are not many university lecturers who would tolerate this type of behavior in their classes. Obviously, letter or essav writine is not easv to monitor in a large lecture hall, but the other foims of disGrbance and disres&t can be readily spotted and curbed if the lecturer is alert. On the other hand, the lecturer who is frequently faced with the above-mentioned behavior should recognize the mensaee are communicatini to him/ clear . ~ - that ~ the ~students ~ her, namely, "You are not meeting our needs!" It would be nice to believe that allstudents are mature and self-motivated, but this just is not the case. Perhaps the t facina all teachers is that of helping most i m ~ o r t a n task studentknderstand the re6vance of the topic being consid: ered. One does not studv thermodvnamics, for example, just because it is listed in-the syllabus and described i n t h e textbook. Students starting to study this topic should be shown how thermodynamics is involved in a multitude of important applications. Experienced lecturers and professional actors are constantly attuned to the reactions of their audiences. Droning away from a prepared text week after week will he guaranteed to turn off even the best students. Good teachers who sense that they are not getting their message across (and this has happened to all of us) must be prepared to modify their approach. Hubert Alyea of Princeton has stated that students can eet much more out of an hour lecture if the lecturer breaks ;he talk into several segments. Twoor three times during an hour lecture Alyea would stop his official presentation, sit down on his ever-present stooi, and chat infbrmally with the class for several minutes. He reports that his relaxed students were then prepared to tackle the most challenging problems. No lecturer should be expected regularly to put on the spectacular productions for which Alyea became famous. But everv chemistrv teacher must consider it part of hisher job to develop a repertoire of demonstrations and anecdotes related to the subject. All of these should be designed to stimulate and arouse the interest of all members of a class. Such activities are as important for college upperclassmen/ women as they are for high school and junior high school students. As a teacher's techniques improve, helshe will be faced less and less with reading, sleeping, and talking during lectures.
Brand and Fisher [1987,64,1035] chose unfortunate examples of chiral objects. The statement that a pair of hands (or a pair of opposite-threaded screws) is "chiral" was misleading and would unnecessarily frustrate students. A clockwise-threaded screw, a right hand, the D-glucose molecule and the letter " R all qualify as chiral objects. Each item is nonsuperimposable on its mirror image, because each item lacks a reflection plane. However, apair of hands is not achiral object. Neither is a air of o~nositelvthreaded screws. When one's hands are held tog&ier pal&-to-pdm, one can easily see the reflection lane. The same is true when a clockwise screw is placed next a counterclockwise screw. Thus, the pair of hands is achiral, and so is the pair of screws. These two illustrations are best reserved for another, more appropriate context. A pair of hands is directly analogous to a meso compound; it is achiral despite having chiral components.
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To the Editor; The right and left hands offer a superb example of a pair of chiral objects. When these are perceived as isolated segments of the body, possessing a mirror-image relationship, with the understanding that they cannot be superimposed, then the true sense of chirality is imparted. When paired together as a single object then a pair of hands is indeed achiral and offers an excellent example of a meso object, as noted by Lechner. Still, as Hinchmann and Hanson have indicated, a proper understanding of the meso ohject requires that one "look beyond the achiral facade of the whole . . .to perceive the localized and opposing chiralities" ( I ) of the segments. The sense with which the pair of hands (or a pair of oppositely threaded screws) is referred to in our review is as isolated chiral objects. When chirality is presented from the perspective we outline, then the illustrations of an individual's hands and a pair of oppositely threaded screws are not misleading but apt. When taught properly, these illustrations should pose no possibility of frustrating any student.
C. LeRoy Darllngton
Davld J. Brand
P.O. Box 303
14 0 Oak Leaf Lane Circle Pines. MN 55014
Temple, ME 04984
358
Joseph H. Lechner Mount Vernon Nararene College 800 Martinsburg Road Mount Vernon, OH 43050
Journal of Chemical Education
