MOLECULAR MODELS IN ORGANIC CHEMISTRY N MINN$.ST OLAF COLLEGE. NORTHFIELD, MINNESOTA
Students in elementary organic chemistry frequently have trouble in visualizing formulas of compounds which are optically active. To represent, on the plane surface of a blackms board, the spatial configuration of a molecule whose carbon atoms may be asymmetric is not always an easy task for the teacher. This difficulty is often encountered in the study of tartaric acid. In order to show more clearly the arrangement of the (COOH), (OH), and (H) groups, the writer found it helpful to make use of a simply constructed model of tartaric acid, appearing in photograph (1).
It is made of stoppers, corks, and glass rod, foundin every laboratory. Number 7 stoppers were used to represent the asymmetric carbon atoms, and these were fitted with glass rods to indicate the valences. Corks of different sizes were used to show the difference between the masses of the groups. It suggests itself immediately that a simple shifting of the corks in the
Vos 6. No.
11
MOLECULAR MODELS IN ORGANIC CHEMISTRY
1985
original d-tartaric model will produce a model representing the 1-tartaric acid, or the meso-tartaric acid. I t was also found helpful to make use of a model constructed similarly, in the study of carbohydrates. The four asymmetric carbon atoms of dextrose can thus be shown clearly (2). By turning the stoppers representing the asymmetric carbon atoms about the central axis, it is possible to illustrate the formula of the 16 isomeric aldohexoses. The reverse side of the dextrose model represents the leuo-glucose molecule (3). The formula for galactose can be illustrated by turning the third stopper about its axis (4). The relationship between dextrose and levulose can also be shown, for the rods representing the doubly linked oxygen can be removed, and a ketohexose can be constructed. Other teachers may find this simple expedient of value in instruction in organic chemistry.
