Cheaply Constructed Models for Conformation Studies Plastic hairpins are found useful far making cheap framework models. Discarded hairpins, bent or broken, may also be used. The pins are cut to a uniform length (3 cm) and if the pieces are bent they are gently warmed over a stove and straightened. To make the tetrahedral carbons a simple wooden gadget is made as follows: Two triangular prisms are cut in soft wood and grooves are made with a saw along the middle of the two sides which subtend the tetrahedral angle of 109" 32'. Guide posts are stuck to these blocks as shown in Figure 1(A and B ) , such that when they are held one over the other crossways (Fig. IC), the grooves will be all tetrahedrally oriented. The plastic bits are held pressed on the grooves by rubber hands and stuck together with a quick drying glue. A convenient cementing glue is prepared simply by dissolving the broken ends of the hairpins in acetone to a viscous solution. For connecting the tetrahedra so made, t o construct various molecules. stiff insulating tape can be used.
Figure 1. Device for making tetrahedra
Figure 2. Device for making octahedra (A) and trigonal bi. pyramids (8).
When the author used these models in the class room, the students were so enthusiastic that they started making them themselves and now many have their own model kits. Models of octahedral and trigonal bipyramidal orientations can also be made out of the hairpins, using a square wooden block with a vertical hole in the center and grooves with the appropriate angles on the top and bottom sides as shown in Figure 2. In making an octahedral atom, for example, a 6-em long piece of plastic is inserted to the halfway paint into the wooden block and four 3-cm pieces, placed on the grooves (Figure ZA), are stuck around its middle. M a d u r a College, Madurai, 625011, India
K. J s g a n n a t h a n
Volume 53, Number 1. January 1976 I 47
