J. Gootjer and 0. Bakuwel Brocades-Stheeman & Pharmacia Amsterdam The Netherlands
Dreiding Model of a Reversible Nitrogen Atom
Dreiding models of molecules, in their original form1 or made out of plastic,%have proved to be very useful in the visualization of conformations. In models of fused polycyclic hydrocarbons a11 possible conformational conversions are easy to realize. However if in a carbocyclic ring system one or both carbon atoms common to two rings are replaced by nitrogen, new conformations become possible, for example, with an inverted configuration of the nitrogen atom. These conformational changes cannot be realized with the rigid Dreiding models. To overcome this, we have modified the model as shown in the figure. Two of the bonds (rods) have a normal rigid bond angle; the third (a tube) ends in a small ring by means of which it can rotate. The ring is made of brass and has been soldered to the stainless steel tube. The boring of the ring (1.6 mm) permits rotation but prevents shifting along the rod. If necessary, shifting may also be prevented by providing the rods with small ridges. Otherwise size and construction are like those of the original Dreiding model.
The new model can be built to fit in existing models of any desired molecule. When used in fused sixmembered rings as an atom rommon to two rings, it automatically takes the tetrahedral form. The new model has proved very useful for demonstrating cow formational changes in quinolizidine derivatives, including yohimbine, reserpine, and other alBaloids with a quinolizidine ring syst.eni.
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DREIDINQ, A. S., Helv. Chim. Aete 42,
1339 (1959).
'FIESER,L. F., J. CAEM.EDOC. 40, 457 (1963).
Volume 42, Number 8, August 1965 / 407
