Use ot Plexigla9 Planes with Molecular Model Kits The use of hall-and-stick model kits to studv the structure and pronerties of organic molecules is very common in be. . and advanced courses in organic and biochemistry. In many cases, one need; to imagine planes slicing through the model of the molecule in order to understand a particular feature of molecular structure. However, many students still have difficulty in visualizing this extra spatial relationship. As a further aid to students, molecular models of organic molecules have been constructed with a clear piece of Plexiglasm attached to serve as a plane of reference. These models can be used much more effectively hy the instructor in class to demonstrate how certain atoms lie in or out of certain planes. The construction of the molecular model attached to the Plexiglas is not difficult but does require careful planning in order to show properly the desired concept or concepts. First ahtain '1s-in. Plexiglas (a local lumber company is a good source). Next, build the molecular model and decide where to locate the Plexiglas plane (or planes) to depict the desired property or properties. The best way to cut the Plexiglas to the correct size is with a table saw. Then with a wood bit in a power drill, drill holes for all places where the plane slices through the balls of the model. These holes need to be somewhat smaller than the halls. A I-in. hole is a good workable size for the 1'14-in. hall and allows one to rotate the hall as it sets in the hole. Next, hond the atoms that will he in the plane together using the stick or spring connectors and set them in the Plexiglas sheet. Drill two '1s-in. holes through the sheet, one an each side of the spring or stick connectors and then attach the model onto the Plexiglas with wire or string. Add the rest of the halls and sticks or spring connectors. The model may now be used in the classroom or labeled and placed on display. Planielna The ~. ~.~~~ " ~"lanes . ~~~~ can he useful in ~racticallv , anv .svstem , where the instructor wishes to use a model to relate the structural featuresoidifferent part* of a mulerule. Someexamples which require only twoof the I-in. hdes in a sheet include the illustration ofconformations ofethane and butane and geometric isomerisms in alkenes. Three hdes drilled with 109' angle between their centers may be used to study chiral centers and actually may help in the assignment of ahsolute confipurations. More complicated systems include planes going through chair and boat conformation of cyclohexane and a c&nparison of the conformations of polyethylene versus polyiso-butylene. Other applications might even include the study of some reaction mechanisms in oreanic chemistrv. Models of molecules that lack a plane of symmetry hut have no asymmetric carbon atoms may also he built with considerable planning. Student comments indicate that the Plexiglas planes added to the molecular modek help show relationships more dearly than in diagrams in texts or in the models without the planes. Plexiglas rarely breaks, can be cut leaving a smooth edge, and is inexpensive and durable. Once built, the models will last for years. ~
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John E. Fulkrod University of Minnesota Technical College, Waseca Waseca, MN 56093
Volume 61
Number 9
September 1984
773
