Rubber Gloves, Rubber Balls and Optical Activity For many students, optical activity proves to be one of the most difficult sections of introductory organic chemistry. I would like to describe several demonstrations aimed a t eliminating some of this difficulty. As mast instructors are aware, there is nothing like a good pair of hands to get a point across. If one considers a molecule containing one chiral carhon atom, there exists two orientations which are "on-superimposable. Depending upon the exact arrangement of the substituents, the chiral carbon (and therefore the molecule as a whole) is designated as being either R or S. Now these enantiomers (asthey are called) may he conveniently represented by a right (R) and left (S) hand. If one considers a molecule with two c h i d carhon atoms, it may be easily shown that there are four possible orientations. By donninga pair of gloves one windsup with the RRisomer on the right hand and the SS isomer on the left. Thestudents can see that the compounds are nonsuperimposable mirror images. By placing the gloves on the other hands, the RS and SR enantiomers may be shown as well as the fact that diastereomers result if a normal hand-glove arrangement (e.g. RR) is compared withan abnormal arrangement (e.g. SR). The useof asecond pair of glovescan be used todemonstrate theexistenee of four sets of ensntiomers for compounds containing three ehiral carbon atoms. This same concept may he used to demonstrate the nature of products resulting from the reaction of chiral molecules with various reagents. If, for example, a raeemic mixture of carboxylie acids reacts withan aehiralalcohol, the product will be a racemie mixture of esters. By using two rubber balls this may he shown. The two hand and hall combinations are nonsuperimpasable mirror images of each other, and therefore will differ only in the direction in which they rotate plane-polarized light. The use of a pair of gloves illustrates the reaction with a reagent which is a raeemie mixture of enantiomers. The gloves may be put on in two different ways, signifying the two sets of enantiomeric products which will be isolated. Finally, if one uses two right or two left hand gloves, the use of a chiral reagent may be illustrated. The products from such a reaction are now no longer mirror images of each other. These diastereomers (RS and SS or RR and SR) will have different physical properties and this fact is used in the process known as resolution, in which a pair of enantiomers are separated by conversion to a pair of diastereomers. Presented at the Atlantic Provinces Inter-University Committee on the Sciences (APICS) Science Education Conference August 20-22,1980, in Sackville, New Brunswick, Canada. Memorial University of Newfoundland S i r Wilfred Grenfell College Corner Brook. Newfoundland A2H GPS Canada
Robert Perkins
Volume 57, Number 11, November 1980 / 809
