F. Vogtle and E. Goldschmitt lnstitut Fir Organische Chernie der UniversitGt 87 Wiirzburg, Am Hubland, Germany
Simple and Inexpensive Orbital Lobe Molecular Models
Pmbably one of the largest expanding fields in education is that of educational aids (models, wall charts, projectors, television), and this is particularly true in the teaching of science subjects. In the teaching of chemistry (especially organic chemistry and biochemistry), for instance, molecular models have become a standard piece of equipment for demonstration purposes, both in the lecture theater and the laborat0ry.l Various types of molecular models are already available (space filling models, framework models, orbital models), but most', if not all, suffer from shortcomings in one way or another. The inadequacies of most models presently marketed became glaringly manifest when delivering lectures on the Woodward-Hoffmann rules and during discussions of exoerimental results (the diaza Cope rearrangement)z in the-laboratory. The need for a set of s i m ~ l e .inex~ensiveand flexible orbital lobe molecular models to be available to each student was immediately apparent. Orbital symmetry controlled reactions can readily be demonstrated with the aid of large demonstration models, e.g., Volz's orbital model^,^ but a much quicker and better understanding of the pericyclic reaction under discussion would be achieved if each student had a small orbital lobe molecular model of his own to handle, similarly, e.g., as is practiced with the well-proven Dreiding models or "framework models"4.5 in stereochemical demonstrations. Sometimes, however, the use of framework models instead of orbital-shaped models is resorted to or even advocated, where, in our opinion, the orbital lobe model is indispensible on didactic grounds, not only for the presentation of a particular topic but also for a closer examination and study thereof. To overcome this situation we have constructed small, plastic, orbital-shaped attachments, which can easily be fitted to the already proven framework molecular models. Figure 1 shows the new plastic orbital lobes (colors: blue and green)= and spherical labelling units that are important for stereochemical studies, together with the bonding elements supplied in the FMM (framework) kit (tetrahedral, trigonal hipyramidal and octahedral valence clus1 For a general review of this topic see Brown, Peter, J. CHEM. EDUC., 48,535 (1971). 1 Vogtle, F., and Goldschmitt, E., Nachr. Chem. Techn., 21,282 (1973):Aneew. Chem., 85, 824 (1973);Angew. Chem. Int. Edn., 12,
767 (1973): 3 "Orbitalmcdelle nach Prof. Dr. H. ~olz' Karlsruhe, available from Karl Kurt Jucheim O.H.G., D 555 Bernkastel-Kues, W. Germany. 4 Framework Molecular Models. Prentice-Hall Inc.. Endewcod . cliffs, N.J. J"Moleeular Orbit Building System", organic and inorganic chemistry; biology and biochemistry, distributed by John Wiley & Sons Ltd, Baffins Lane, Chiehester, Sussex, England and by Lehrmittelverlag Harrasser + Uherla, 858 Bayreuth, Ottostr. 5, Germany. 6 Woodward, R. B., and Hoffmann, R., Angew. Chem. I n t . Edn., 8, 781 (1969); "The Conservation of Orbital Symmetry," Academic Press, New York, 1910. ?Also, a variety of expanded polyet'hylene orbital models are available from Science Related Materials Company, Jamesville, Wisconsin 53545.
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Figure 1. New orbital lobes and framework units.
Figure 2. Thermally ailawed conrotatory buta-1.3-diene cyclobutene elecIr~C~Clizatio".
ters, pins, angles, color tubing), which enable construction of any desired type of organic molecule. No further parts are required; this can readily be appreciated from Figure 2, which shows the use of the new orbital lobe attachments and the framework units for demonstration of the electrocyclic ring closure: buta-1,3-diene cyclobutene. Apart from ease of manipulation and manageable size (a large number of individual units can be carried around in the workaday briefcase), such real orbital models-being readily constructed by simple attachment of plastic orbital lobes to framework building units-ffer numerous additional advantages over presently available models: they are robust and even large size molecular models do not break apart; the bonding is rigid in the sense that a particularly chosen conformation does not change on passing the model from hand to hand. The flexibility of the plastic tubes enables models of small rings (cyclopropane, cyclobutane) and other strained molecules to be constructed, the symmetry of transitional states to be studied. and the bond lengths to he individually. adiusted. The . representation of heteroatoms or substituents presents no Droblems. for the colored framework tubes can be used for this purp&e. The orbital lobes may he manufactured7 from lightweight, soft (porous) plastic or (foam) rubber material thus rendering them more flexible, a desirable feature for
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the demonstration of transhybridization, e.g., in SN reactions or in the study of antarafaeial additions. Other refinements and slight modifications are possible and have
been tried out. Anyone desiring further details about these simple and inexpensive orbital lobe molecular models is invited to write to the authors.
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Volume 51, Number 5. May 1974
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