Lojos MCszaros
A Magnetic Molecular Model
University of Szeged Szeged, Hungary
A
model of the ethane molecule has been constructed which will demonstrate qualitatively the low energy barrier in free rotation about the C-C bond. This is accomplished by attaching the spheres representing H atoms to the C atoms by means of small identical rods of magnetized steel. The same poles of the magnets are inserted in the H spheres. The C-C bond is represented by a spike firmly imbedded in one C
cr
0. Figure 2.
Figure 1.
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Journal o f Chemical Education
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sphere hut going through a hole in the second C sphere to terminate in a plastic cone as shown in Figure 1. This supports the CH3 and allows rotation with a minimum of friction, much as the needle of a compass is constructed. The CH3 thus supported will orient itself in a staggered configuration because of the repulsions of the like poles of the magnets in the H spheres. A sensitive dynamometer can be used to measure the force required to rotate the CH, unit through a complete 360' turn. Figure 2 shows a plot of this force as a function of the rotational angle. The three maxima and minima of this curve represent the three potential energy maxima and minima associated with the rotation of one CHawith respect to the other CH3in ethane. Models of larger paraffins have been constructed on the same principle. Gravitational effects interfere, but if the models are suspended in a mildly agitated liquid of a density identical with the halls, they assume the orientation of a structure with minimum potential energy.
