An Expanded Fieser Model Suitable for a Large Clawroom The value ofthe use of models in teaching11 well recognized. The particular problem ofthe availability ofinexpensive large models has been addressed several times in recent years in this Journol in regard to, for example, hydrogen bondingin pmteins' and in the use of models in conjunction with a n overhead p m j e c t ~ rIn . ~organic chemistry, one area in which models are indispensable is in introducing the mnformational analysis of cyclopentane and eyelohexme rings. A large sturdy model capable of undergoing repeated conformational changes in these rings without falling apart, the Petersen-Cenco model, used a threaded mnnection between bands and atoms. It was relatively expensme and is no longer a ~ a i l a b l eA . ~"giant-size" framework type model available from Aldrich Chemical Co., Inc4 clearly shows axial andequatorial bondcon cyclohexane but the model does tend to come apart on repeated chair-boat-chair conformational conversions. I t uses friction to hold the bonds into receptors on the atoms. Also, t h e s e t i s not inexpensive. The wellknown Fieser models, also available fmm Aldrich, are inexpensive, reasonably durable and very clearly show axial and equatorial bonds. They use a snap-loek type fitting to connect bonds to atoms. Their major shortcoming is their size. A cyclohexane ring in the chair mnformation is only 15 cm fmm C-1 to C-4 and not L 4.5mm Dia. L4.76mm Dia. 4.65.m Dia. A useful i n even a modest size lecture (0.177") (0.18s'') (0,183'') hall.We have found i t possible ta inexpensively expand Fieser models to retain the desirable features and to overcome the s u e dwadvanta~? I FIESER MODEL EXTENSION Three carbon tetrahedra must be sacnMAT'L: 4 . 7 6 ~ . 3/16") Dia. fimd to ohrnm them SIX thin-walled olumlBRASS 'RLD num tubes. These six tubes become bond extenders when attached with Loctite RC16t7" to one end of 3116-in. brass rods. The other end of each rod is similar attached to an aluminum tube on a carbon atom. The brass rods need to be turned a t both ends (see illustration) in oder t into the tuhes. .n . fit ~. ~~~~- -~ The -~~~orientation must be such that the new reemtor end dunlicates the recentor end of the original earhon atom. When the carbon atoms are connected in the usual fashion the fivemembered rrng and the six-memhered nng both show all the stereoehemieal features of the unmodified models but are larxeer. For instance. m t h a n extension of 5 5 em hatween two tubes the C-l tu C-4 distance is approximately 33 cm. The only disndvantagc we have noted so far is that the expanded model is more fragile than the normal Fieser model. The plastic carhon atoms in the extended rings are subjected to more stress d-ng a rmC flip and some rare is recommended. The two hands remaminx on each carbon finally rcquire extenders of lightweight plastic rods or tubes to indicate the correct lenmh of the G H bonds relnrive tn the C-C honds. It r.i useful tu make all the axlal bonds one color and the equatorial bonlds a different mlor. The addition of plastic spheres to represent hydrogen atoms completes the model. ~~~~~~~~~~~~
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1Bricklev. M.: Silva. R.A. J. Chem. Educ. 1985, 62.1077-1078 RS n J Chem Eadc 1986 63.516517. 'petersen, O R :Centra M ch gan Unlvers I,, personal cornrnmicalion. 1990. 'Ator cn Cnemca Comoanv. nc ,1001 Wesl Sa nl Pad Aven~e.M wawee. W1 53233. ' ~ r a n e . ~-:2 .
Alfred S. Levlnson Rudolph Zupan Portland State University PO Box 751 Portland, OR 97207
Volume 69
Number
5 May 1992
369
